Thailand

Thailand was known by outsiders before 1939 as Siam. According to George Cœdès, the word Thai (ไทย) means 'free man' in the Thai language, "differentiating the Thai from the natives encompassed in Thai society as serfs". According to Chit Phumisak, Thai (ไท) simply means 'people' or 'human being'; his investigation shows that some rural areas used the word "Thai" instead of the usual Thai word khon (คน) for people. According to Michel Ferlus, the ethnonyms Thai-Tai (or Thay-Tay) would have evolved from the etymon *k(ə)ri: 'human being'.

Thais often refer to their country using the polite form prathet Thai (Thai: ประเทศไทย). They also use the more colloquial term mueang Thai (Thai: เมืองไทย) or simply Thai; the word mueang, archaically referring to a city-state, is commonly used to refer to a city or town as the centre of a region. Ratcha Anachak Thai (Thai: ราชอาณาจักรไทย) means 'kingdom of Thailand' or 'kingdom of Thai'. Etymologically, its components are: ratcha (Sanskrit: राजन्, rājan, 'king, royal, realm'), ana- (Pali āṇā 'authority, command, power', itself from the Sanskrit आज्ञा, ājñā, of the same meaning), and -chak (from Sanskrit चक्र cakra- 'wheel', a symbol of power and rule). The Thai National Anthem (Thai: เพลงชาติ), written by Luang Saranupraphan during the patriotic 1930s, refers to the Thai nation as prathet Thai (Thai: ประเทศไทย). The first line of the national anthem is: prathet thai ruam lueat nuea chat chuea thai (Thai: ประเทศไทยรวมเลือดเนื้อชาติเชื้อไทย), 'Thailand is founded on blood and flesh'.

The former name Siam may have originated from Sanskrit श्याम (śyāma, 'dark') or Mon ရာမည (rhmañña, 'stranger'), probably the same root as Shan and Assam. The word Śyâma is possibly not the true origin, but a pre-designed deviation from its proper, original meaning. Another theory is the name derives from the Chinese calling this region 'Xian'. Yoneo Ishii traces the European form to a compound. After Xiān and Luó hú were joined in 1349, Chinese records call the result Xiānluó hú (暹羅斛), later shortened to Xiānluó. The ancient Khmers used Siam to refer to people settled in the west Chao Phraya River valley surrounding the ancient city of Nakhon Pathom in present-day central Thailand; it may originate from the name of Krishna, who was also called Shyam. The Wat Sri Chum Inscription, dated in the 13th century CE, mentions Phra Maha Thera Sri Sattha came to restore Phra Pathommachedi at the city of Krishna (Nakhon Pathom) in the early era of the Sukhothai Kingdom.

The signature of King Mongkut (r. 1851–1868) reads SPPM (Somdet Phra Poramenthra Maha) Mongkut Rex Siamensium (Mongkut, King of the Siamese). This usage of the name in the country's first international treaty gave the name Siam official status, until 24 June 1939 when it was changed to Thailand.

=== Prehistory and origins ===

There is evidence of continuous human habitation in what is now Thailand from 20,000 years ago to the present day. The earliest evidence of rice growing is dated at 2,000 BCE. The area comprised part of the Maritime Jade Road, a trading network which existed for 3,000 years, between 2000 BCE to 1000 CE. Bronze appeared c. 1,250–1,000 BCE. The site of Ban Chiang in northeast Thailand currently ranks as the earliest known centre of copper and bronze production in Southeast Asia. Iron appeared around 500 BCE.

The kingdom of Funan was the first and most powerful Southeast Asian kingdom, established in the 2nd century BCE. The Mon people established the principalities of Dvaravati and Kingdom of Hariphunchai in the 6th century. The Khmer people established the Khmer Empire, centred in Angkor, in the 9th century. Tambralinga, a Malay state controlling trade through the Malacca Strait, rose in the 10th century. The Indochina peninsula was heavily influenced by the culture and religions of India from the time of Funan to the Khmer Empire.

The Thai people are of the Tai ethnic group, characterised by common linguistic roots. Chinese chronicles first mention the Tai peoples in the 6th century BCE. While there are many assumptions regarding the origin of Tai peoples, David K. Wyatt, a historian of Thailand, argues that their ancestors who inhabit Laos, Thailand, Myanmar, India, and China came from the Điện Biên Phủ area between the 5th and the 8th century. Thai people began migrating into present-day Thailand gradually from the 6th to 11th century, which Mon and Khmer people occupied at the time. Thus Thai culture was influenced by Indian, Mon, and Khmer cultures. Tai people intermixed with various ethnic and cultural groups in the region, resulting in many groups of present-day Thai people. Genetic evidences suggest that ethnolinguistics could not accurately predict the origins of the Thais. Sujit Wongthes argues that Thai is not a race or ethnicity but a culture group.

According to French historian George Cœdès, "The Thai first enter history of Farther India in the eleventh century with the mention of Syam slaves or prisoners of war in Champa epigraphy", and "in the twelfth century, the bas-reliefs of Angkor Wat" where "a group of warriors" are described as Syam, though Cham accounts do not indicate the origins of Syam or what ethnic group they belonged to. The origins and ethnicity of the Syam remain unclear, with some literature suggesting that Syam refers to the Shan people, the Bru people, or the Brau people. However, Mainland Southeast Asian sources from before the 14th century primarily used the word Syam as an ethnonym, referring to those who belonged to a separate cultural category different from the Khmer, Cham, Bagan, or Mon. This contrasts with the Chinese sources, where Xian was used as a toponym.

Theoretically, Tai-Kadai-speaking people formed as early as the 12th century BCE in the Yangtze basin. Some groups later migrated south to Guangxi. However, after several bloody centuries against Chinese influence in Guangxi between 333 BCE and the 11th century, hundreds of thousands of Tais were killed, thus, Tai people began to move southwestward along the rivers and over the lower passes into the mountain north of Southeast Asia and river valleys in present-day Assam of India. Some evidence indicates that the ancestors of Tai people migrated en masse southwestwards out of Yunnan only after the 1253 Mongol invasion of Dali; however, it is not generally accepted. A separate line of movement has been proposed for the middle Mekong. Tatsuo Hoshino places Tai-speaking groups attested in northern Champa, in what are now Nghệ An and Thanh Hóa, moving west into the central Mekong valleys during the 5th and 6th centuries and spreading across Isan and into the Chao Phraya basin over the centuries that followed, taking Haudricourt's 3rd century as the earliest possible date for a westward movement of tonal Tai out of Chinese-controlled Vietnam. Tais defeated indigenous tribes and emerged as the new power in the new region. As a result, several Tai city-states were established, scattered from Điện Biên Phủ in present-day northwestern Vietnam and highland Southeast Asia to northeastern India.

According to the Simhanavati legend given in several chronicles, the first Tai city-state in northern Thailand, Singhanavati, was founded around the 7th century. However, several modern geology and archaeology studies found that its centre, Yonok Nahaphan, dates from 691 BCE–545 CE; this roughly coincides with the establishment of Shan states, another Tai's federated principalities in the present-day northeast Myanmar. as well as Muang Sua (Luang Prabang) in the east.

After Singhanavati was submerged below Chiang Saen Lake by an earthquake in 545, the survivors then founded a new seat at Wiang Prueksa. The kingdom lasted for another 93 years. Ngoenyang was established as the successor of Singhanavati in 638 by Lavachakkaraj, also centred in Wiang Prueksa (present-day Mae Sai District, Chiang Rai). Its seat was moved to Chiang Mai in 1262 by King Mangrai, which is considered the foundation of the Lan Na kingdom. Mangrai unified the surrounding area and created a network of states through political alliances to the east and north of the Mekong. His dynasty ruled for the next two centuries, expanding territory southward and annexing the Hariphunchai of Dvaravati in 1292.

In the late 10th century, Tai people began to migrate further south. By the 12th century several cities in this area, such as Songkwae, Sawankhalok, and Chakangrao, were ruled by the Tai people, eventually launching several battles against the Mon of Lavo, who had been under Chenla and Khmer influences since the 7th century, thus bringing the establishment of the Tai people's independent state, Sukhothai Kingdom, in the upper Chao Phraya River valley in 1238.

The earliest conflict between Tai people and the preexisting ethnics was recorded in the mid-4th century when the ruler of Singhanavati, Pangkharat, forcibly lost the seat at Yonok to King Khom from Umongasela (present-day Fang). He then fled to Vieng Si Tuang (เวียงศรีทวง; present-day Wiang Phang Kham, Mae Sai district) but had to send tributes to Yonok annually until his son, Phrom, took back Yonok and expelled King Khom from Umongasela. Phrom also marched the troops south to occupy Chakangrao from the enemy as well as founding the city of Songkwae. Some historians suggest that Lavo's capital, Lopburi, was once seized by Phrom. In contrast, Tai people instead established relationships with Mon via royal intermarriages.

The Chao Phraya River was home of the Mon Dvaravati culture, which prevailed from the 7th century to the 10th century. Samuel Beal discovered the polity among the Chinese writings on Southeast Asia as "Duoluobodi". During the early 20th century, archaeological excavations led by George Coedès found Nakhon Pathom Province to be a centre of Dvaravati culture. The two most important sites were Nakorn Pathom and U Thong (in modern Suphan Buri Province). The inscriptions of Dvaravati were in Sanskrit and Mon using the script derived from the Pallava alphabet of the South Indian Pallava dynasty.

It is believed that the Dvaravati borrowed Theravada Buddhism through its contacts with Sri Lanka, while the ruling class participated in Hindu rites. Dvaravati art, including the Buddha sculptures and stupas, showed strong similarities to those of the Gupta Empire of India. The eastern parts of the Chao Phraya valley were subjected to a more Khmer and Hindu influence as the inscriptions are found in Khmer and Sanskrit. Dvaravati was a network of city-states paying tribute to more powerful ones according to the mandala political model. Dvaravati culture expanded into Isan as well as south as far as the Kra Isthmus. Dvaravati culture lost its influence around the tenth century when they submitted to the more unified Lavo-Khmer polity.

Around the 10th century, the city-states of Dvaravati merged into the mandalas of Lavo (modern Lopburi) and Suvarnabhumi (modern Suphan Buri). According to a legend in the Northern Chronicles, in 903, or in 927 on other readings of the same chronicles, a king of Tambralinga invaded and took Lavo and installed a Malay prince on the Lavo throne. The Malay prince was married to a Khmer princess who had fled an Angkorian dynastic bloodbath. The son of the couple contested the Khmer throne and became Suryavarman I, thus bringing Lavo under Khmer domination through marital union. Suryavarman I expanded into the Khorat Plateau (later styled "Isan"), constructing many temples.

Angkor lost Lavo to Suphannabhum princes in 1052, and the seat moved from Lavapura to Ayodhya in the 1080s under Narai I. Angkor moved to recover its influence in 1181, when Jayavarman VII appointed his kinsman Narupatidnavarman to govern Lavapura. Due to this political pressure, Tai ruler Sri Thammasokkarat (ศรีธรรมโศกราช), who was also from Si Satchanalai, fled to Nakhon Si Thammarat, where his descendants ruled Tambralinga into the late 13th century. Zhou Daguan, sent to Angkor by the Yuan dynasty in 1296–7, reports in The Customs of Cambodia that the Siamese exerted significant influence over Lavapura and appeared in numbers at Yaśodharapura.

However, Lavapura was probably taken back by a Tai royal from Phraek Si Racha (แพรกศรีราชา; present-day Sankhaburi) in the 13th century. Angkorian power meanwhile waned amid weak rule and feuding. In 1238 a Siamese coalition under Bang Klang Hao recaptured Sukhothai and re-established it as an autonomous polity. The event is conventionally treated as the kingdom's foundation, although Siamese rulers are recorded at the city earlier.

The earliest known evidence of the Siam people comes from stone inscriptions found in Angkor Borei of Funan, dated to 661 CE. The slave's name is mentioned as "Ku Sayam" meaning "Sayam female slaves" (Ku is a prefix used to refer to female slaves in the pre-Angkorian era), and the Takéo inscriptions (K.79) written in 682 during the reign of Bhavavarman II of Chenla also mention Siam Nobel: Sāraṇnoya Poña Sayam, which was transcribed into English as: the rice field that was given to the poña (noble rank) who was called Sayam (Siam).

The name has also been sought in the Chinese record of the middle Mekong. Tatsuo Hoshino reads several polities named there in the Tang annals as early Tai or Siamese states lying on the trans-Mekong routes that linked Champa with the Chao Phraya basin, arguing from their reported customs, their fortifications and their military organisation. He supports the reading with the Chinese renderings of their names: in Wen Dan (文單) he takes wén for Cantonese man, used across Daic dialects for a village, and dān for a syllable he reads as sin or sham, possibly the proto-Siamese name, while Cān Bàn (参半) he reads as sam, which he links to Siam, with bun as a reflex of the Sanskrit pūra. Hiram Woodward regards the linguistic argument as tendentious and holds that it should be used neither to support nor to invalidate Hoshino's geographical conclusions.

The Song Huiyao Jigao (960–1279) indicate Siamese people settled in the west central Thailand and their state was called Xiān guó (Chinese: 暹國), while the eastern plain belonged to the Mon of Lavo (Chinese: 羅渦國), who later fell under the Chenla and Khmer hegemony around the 7th–9th centuries. Those Mon political entities, which also included Haripuñjaya in the north and several city-states in the northeast, are collectively called Dvaravati.

However, the states of Siamese and Lavo were later merged via the royal intermarriage and became Ayutthaya Kingdom in the mid-14th century, while the southwestern Isan principalities, centred in Phanom Rung and Phimai, later pledged allegiance to Siamese's Ayutthaya during the reign of Borommarachathirat II. The remaining principal city-states in Isan region became Lan Xang around 1353 after the twin cities of Muang Sua (Luang Prabang) and Vieng Chan Vieng Kham (Vientiane) became independent following the death of the Sukhothai king Ram Khamhaeng.

According to the Wat Kud Tae inscription, dated c. 7th century, during the period that Lavo was strongly influenced by the Chenla, the Siamese in the west also established a royal intermarriage with Chenla as Sri Chakatham, prince of Sambhuka (ศามภูกะ, in the present-day Ratchaburi province), married to a princess of Isanavarman I, and two mandalas then became an ally. After Chenla sieged Funan and moved the centre to Angkor, both Siamese and the Angkorian attacked Vijaya of Champa in 1201 during the reign of Jayavarman VII.

After the decline of the Khmer Empire and Kingdom of Pagan in the early 13th century, various states thrived in their place. The domains of Tai people existed from the northeast of present-day India to the north of present-day Laos and to the Malay Peninsula. During the 13th century, Tai people had already settled in the core land of Dvaravati and Lavo Kingdom to Nakhon Si Thammarat in the south. There are, however, no records detailing the arrival of the Tais.

Around 1240, Pho Khun Bang Klang Hao, a local Tai ruler, rallied the people to rebel against the Khmer. He later crowned himself the first king of Sukhothai Kingdom in 1238. Thai historians count Sukhothai as the first kingdom of Thai people. Sukhothai expanded furthest during the reign of Ram Khamhaeng. However, it was mostly a network of local lords who swore fealty to Sukhothai, not directly controlled by it. He is believed to have invented Thai script and Thai ceramics were an important export in his era. Sukhothai embraced Theravada Buddhism in the reign of Maha Thammaracha I.

According to the most widely accepted version of its origin, the Ayutthaya Kingdom rose from the earlier, nearby Lavo Kingdom and Suphannaphum with Uthong as its first king. Chris Baker and Pasuk Phongpaichit count four towns of the lower plain that had each sent missions to China in its own name before the union, adding Ayodhya itself and Phetchaburi to those two. Ayutthaya was a patchwork of self-governing principalities and tributary provinces owing allegiance to the King of Ayutthaya under the mandala system. Its initial expansion was through conquest and political marriage.

Before the end of the 15th century, Ayutthaya invaded the Khmer Empire three times and sacked its capital Angkor. The steady rise of the Ayutthaya Kingdom marked a major geopolitical shift, eventually allowing Ayutthaya to eclipse the Khmer Empire and assume the mantle of regional dominance in mainland Southeast Asia. Constant interference of Sukhothai effectively made it a vassal state of Ayutthaya and it was finally incorporated into the kingdom. Baker and Pasuk reject that account, holding that it applies a model of sovereignty foreign to the region, in which a defeated ruler remained a king and an overlord imposed no administration, and setting in its place the marriages by which Borommaracha I, Intharacha and Borommarachathirat II each took a daughter of Li Thai. Borommatrailokkanat brought about bureaucratic reforms which lasted into the 20th century and created a system of social hierarchy called sakdina, where male commoners were conscripted as corvée labourers for six months a year. Ayutthaya was interested in the Malay Peninsula but failed to conquer the Malacca Sultanate, which was supported by the Chinese Ming dynasty.

European contact and trade started in the early-16th century, with the envoy of Portuguese duke Afonso de Albuquerque in 1511. Portugal became an ally and ceded some soldiers to King Rama Thibodi II. The Portuguese were followed in the 17th century by the French, Dutch, and English. Rivalry for supremacy over Chiang Mai and the Mon people pitted Ayutthaya against the Burmese Kingdom. Several wars with its ruling Taungoo dynasty starting in the 1540s in the reign of Tabinshwehti and Bayinnaung were ultimately ended with the capture of the capital in 1570. Then a brief period of vassalage to Burma until Naresuan proclaimed independence in 1584 followed.

Ayutthaya sought to improve relations with European powers for many successive reigns. The kingdom especially prospered during cosmopolitan Narai's reign (1656–1688), when some European travellers regarded Ayutthaya as an Asian great power, alongside China and India. However, growing French influence later in his reign was met with nationalist sentiment and eventually led to the Siamese revolution of 1688. Despite the revolution, overall relations remained stable, with French missionaries still actively preaching Christianity.

After a bloody period of dynastic struggle, Ayutthaya entered what has been called the Siamese "golden age", a relatively peaceful episode in the second quarter of the 18th century where art, literature, and learning flourished. There were seldom foreign wars, apart from conflict with the Nguyễn lords for control of Cambodia starting around 1715. The last fifty years of the kingdom witnessed bloody succession crises, where there were purges of court officials and able generals for many consecutive reigns. In 1765, a combined 40,000-strong force of Burmese armies invaded it from the north and west. The Burmese under the new Alaungpaya dynasty quickly rose to become a new local power by 1759. After a 14-month siege, the capital city's walls fell and the city was burned in April 1767.

The capital and many of its territories lay in chaos after the war. The former capital was occupied by the Burmese garrison army and five local leaders declared themselves overlords, including the lords of Sakwangburi, Phitsanulok, Pimai, Chanthaburi, and Nakhon Si Thammarat. Chao Tak, a capable military leader, proceeded to make himself a lord by right of conquest, beginning with the legendary sack of Chanthaburi. Based at Chanthaburi, Chao Tak raised troops and resources, and sent a fleet up the Chao Phraya to take the fort of Thonburi. In the same year, Chao Tak was able to retake Ayutthaya from the Burmese only seven months after the fall of the city.

Chao Tak then crowned himself as Taksin and proclaimed Thonburi as temporary capital in the same year. He also quickly subdued the other warlords. His forces engaged in wars with Burma, Laos, and Cambodia, which successfully drove the Burmese out of Lan Na in 1775, captured Vientiane in 1778 and tried to install a pro-Thai king in Cambodia in the 1770s. In his final years there was a coup, supposedly caused by his "insanity", and eventually Taksin and his sons were executed by his longtime companion General Chao Phraya Chakri (the future Rama I). He was the first king of the ruling Chakri dynasty and founder of the Rattanakosin Kingdom on 6 April 1782.

Under Rama I, Rattanakosin successfully defended against Burmese attacks and put an end to the incursions. He also created suzerainty over large portions of Laos and Cambodia. In 1821, Briton John Crawfurd was sent to negotiate a trade agreement with Siam—the first sign of an issue which was to dominate 19th century Siamese politics. Bangkok signed the Burney Treaty in 1826, after the British victory in the First Anglo-Burmese War.

Anouvong of Vientiane, who mistakenly held the belief that Britain was about to launch an invasion of Bangkok, started the Lao rebellion in 1826, which was suppressed. Vientiane was destroyed, and a large number of Lao people were relocated to Khorat Plateau as a result. Bangkok also waged several wars with Vietnam, where Siam successfully regained hegemony over Cambodia.

From the late 19th century, Siam tried to rule the ethnic groups in the realm as colonies. In the reign of Mongkut (1851–1868), who recognised the potential threat Western powers posed to Siam, his court contacted the British government directly to defuse tensions. A British mission led by John Bowring, governor of Hong Kong, led to the signing of the Bowring Treaty, the first of many unequal treaties with Western countries. This, however, brought trade and economic development to Siam. The unexpected death of Mongkut from malaria led to the reign of underage King Chulalongkorn, with Somdet Chaophraya Sri Suriwongse (Chuang Bunnag) acting as regent.

Chulalongkorn initiated centralisation, set up a privy council, and abolished slavery and the corvée system. The Front Palace crisis of 1874 stalled attempts at further reforms. In the 1870s and 1880s, he incorporated the protectorates up north into the kingdom proper, which later expanded to the protectorates in the northeast and the south. He established twelve krom in 1888, which were equivalent to present-day ministries. The 1893 Franco-Siamese crisis erupted, caused by French demands for Laotian territory east of Mekong.

Thailand is the only Southeast Asian state never to have been colonised by a Western power, in part because Britain and France agreed in 1896 to make the Chao Phraya valley a buffer state. Not until the 20th century could Siam renegotiate every unequal treaty dating from the Bowring Treaty, including extraterritoriality. The advent of the monthon system marked the creation of the modern Thai nation-state. In 1905, there were unsuccessful rebellions in the ancient Patani area, Ubon Ratchathani, and Phrae in opposition to an attempt to blunt the power of local lords.

The Palace Revolt of 1912 was a failed attempt by Western-educated military officers to overthrow the Siamese monarchy. Vajiravudh responded by propaganda for the entirety of his reign, which promoted the idea of the Thai nation. In 1917, Siam joined the First World War on the side of the Allies. In the aftermath, Siam had a seat at the Paris Peace Conference and gained freedom of taxation and the revocation of extraterritoriality.

A period of wasteful spending by King Vajiravudh followed by the Great Depression brought economic hardships on Thailand, with sharply falling rice prices, a significant reduction in public spending, eroded confidence in the monarchy, and discontent among aristocratic supporters all contributing to the destabilisation of the Chakri dynasty. These conditions spurred on the bloodless Siamese revolution of 1932, in which the Khana Ratsadon movement forced King Prajadhipok to sign the country's first constitution, thereby ending centuries of feudal and absolute monarchy. Power was partially ceded to a democratic government, but it would not last a year before the rise of significant military influence in Thai political affairs.

In 1933, Prime Minister Phraya Mano led a counter-revolutionary rebellion to reinstate an absolute monarchy under Prajadhipok. This was followed by a military coup that installed Phraya Phahon – a leader of the 1932 revolution – as prime minister. Prajadhipok's conflict with the government eventually led to his abdication, and the new military-led government selected Switzerland-raised Ananda Mahidol to be the new king.

The armed wing of Khana Ratsadon gradually came to dominate Siamese politics. Military strongman Plaek Phibunsongkhram, often known as "Phibun", became premier in 1938 and launched a campaign of political repression that saw the execution of both monarchists and pro-democracy liberals. His government adopted Thai nationalist, pro-Westernisation, anti-royalist, Irredentist, anti-Chinese and anti-French policies.

In 1939, Phibun changed the country's name from "Siam" to "Thailand". This coincided with the rise of fascist ideology in Thailand, with the name change reflecting policies that prioritised the needs of ethnic Thais over those of minorities like the Thai Chinese. Phibun was an admirer of Benito Mussolini, and he imposed 12 Thai cultural mandates requiring citizens to obey nationalist norms such as saluting the flag, knowing the national anthem, speaking only Thai, and wearing Western clothing. In October 1940, months after fall of France to Nazi Germany, Phibun launched an opportunistic invasion of territories lost to French Indochina during the reign of King Chulalongkorn. The invasion was a success, with Thailand additionally gaining some Lao and Cambodian territories.Japan, which had also been invading French Indochinese territories, brokered a ceasefire that forced France to give up several territories to Thailand.

On 8 December 1941, the Japanese Empire launched an invasion of Thailand, and fierce fighting broke out in southern Thailand before Phibun ordered an armistice and joined the Axis powers just five hours later. Japan was granted free passage through Thai territory, and on 21 December Thailand and Japan signed a military alliance, with a secret protocol wherein the Japanese government agreed to help Thailand gain further territories throughout southeast Asia. The Thai government then declared war on the United States and the United Kingdom. The United Kingdom, whose colony Malaya was under immediate threat from Thai forces, responded in kind, but the United States refused to declare war and ignored Thailand's declaration. The Free Thai Movement was launched both in Thailand and abroad to oppose the Thai government and Japanese occupation. After the war ended in 1945, Phibun was ousted and Thailand signed formal agreements to end the state of war with the Allies.

In June 1946, King Ananda was found dead under mysterious circumstances, and his younger brother Bhumibol Adulyadej ascended to the throne. This period of liberal rule was brief, with Phibun launching another military coup to take power in 1947. In his second term as prime minister, Phibun pursued an alliance with the United States by undertaking a campaign of domestic anti-communism, aiding the United States in the Korean War, and helping to establish the US-aligned Southeast Asia Treaty Organization (SEATO) in 1954. Following a tour of Europe and the US in 1955 where he was impressed by democratic practices like freedom of speech, Phibun began to democratise Thai politics by allowing new political parties and trade unions to form, opening public forums, granting amnesty to former political opponents, and preparing Thailand for its first free elections. However, these practices likely aroused opposition to Phibun's dictatorial legacy, and the US supported his final ouster in 1957.

Field Marshal Sarit Thanarat took power by coup in 1957, and he proceeded to reverse Phibun's democratic reforms and ban the Khana Ratsadon party from politics. His rule from 1959 to 1963 was autocratic; he built his legitimacy around the god-like status of the monarch and by channelling the government and public's loyalty to the king. Though Phibun had been criticised for his close relationship to the United States, Sarit also aligned himself with them and militarily supported the United States in the Vietnam War in 1961, leading a simultaneous campaign of anti-communist mass killings in Thailand that continued under his successor Thanom Kittikachorn.

The Sarit and Thanom periods coincided with significant modernisation and Westernisation of Thai society. Rapid urbanisation occurred as the rural populace sought work in growing cities like Bangkok. Economic development and public education enabled the rise of an urban middle class. The growth of this economy based on wage labour rather than subsistence agriculture resulted in increased class consciousness and sympathies to the Communist Party of Thailand, while university-educated students formed movements against the military dictatorship.

In October 1973, a popular democratic uprising against the Thanom government began to bring about an end to Thailand's military regime. In response to mass killings of protesters, King Bhumibol installed Sanya Dharmasakti as prime minister, marking the first time that the king had intervened in Thai politics directly since 1932. The aftermath of the event marked a short-lived parliamentary democracy.

With new democratic institutions limited in their capability to solidify power and pass reforms, the three years after the uprising were marked by political and economic instability. For the next year, street protests were almost daily events. Right-wing fears of a communist takeover of Thailand grew following the captures of South Vietnam, Cambodia, and Laos by communist insurgents. These factors culminated in the Thammasat University massacre in October 1976, in which police and right-wing mobs massacred students protesting the return of Thanom Kittikachorn to Thai politics. A military coup d'état on that day brought Thailand a new ultra-right-wing military government which cracked down on media outlets, government officials, and intellectuals, engendering a communist insurgency. Another military coup the following year installed a more moderate military government, which offered amnesty to some communist fighters in 1978.

Military figure Prem Tinsulanonda was appointed prime minister from in 1980. He oversaw the beginning of a period of significant economic growth and democratisation throughout the 1980s. Prem's premiership was often referred to as "premocracy" because it involved semi-democratic practices such as a Parliament composed of an all-elected House and an all-appointed Senate. Prem's constitutionalist political approach aided with a transition away from military rule and a negotiated end to the Communist insurgency by 1983. He maintained political stability via a close relationship with King Bhumibol, who helped to foil two military coups in attempts against Prem in 1981 and in 1985.

In 1988, Thailand saw its first freely-elected prime minister since the 1976 coup. Chatichai Choonhavan ruled for 3 years before being overthrown in a coup that ushered in two years of military rule under the National Peace Keeping Council. One of the coup leaders, Suchinda Kraprayoon, was nominated as prime minister for the majority coalition government after the March 1992 general election. This caused a popular demonstration in Bangkok, which ended with a bloody military crackdown known as Black May. King Bhumibol intervened in the event, granting amnesty to the belligerents and forcing the resignation of Suchinda.

Free elections were once again held in September 1992, bringing the neoliberal Democrat Party to power. Power passed between various neoliberal parties throughout the decade, who all had a hand in drafting the 1997 "People's Constitution." Spurred on by the events of Black May, the constitution explicitly acknowledged several human rights and established several government and electoral accountability measures, including the creation of a fully-elected bicameral legislature.

The neoliberal government's attempt to peg the Thai baht to the United States dollar induced the 1997 Asian financial crisis, crashing regional economies and ending nearly 40 years of uninterrupted economic growth in Thailand. To cover a shortage of foreign currency and investments, which had come primarily from Japan, Chavalit Yongchaiyudh's government took out a $17 billion International Monetary Fund loan in US dollars. To satisfy the conditions of the loan, Thailand underwent a series of austerity measures until the loan was repaid in 2003.

The crisis brought on the ascendancy of the populist Thai Rak Thai Party, whose base consisted primarily of indebted rural workers. Prime Minister Thaksin Shinawatra's policies were successful in reducing rural poverty and providing universal healthcare. However, Thaksin was viewed by opponents among the Thai upper and upper middle classes as a corrupt populist who was destroying the middle class in order to favour himself and the rural poor. Additionally, his rural poverty policies directly conflicted with King Bhumibol's recommendations, drawing the ire of royalists, a powerful faction in Thailand. Thaksin also faced crises in the form of the southern Thailand insurgency, which escalated starting from 2004, and the 2004 Indian Ocean earthquake and tsunami which claimed around 8,000 lives in Thailand.

Massive protests against Thaksin led by the reactionary People's Alliance for Democracy (PAD) started in his second term as prime minister, and the monarchy and the military eventually agreed to oust him. The crisis peaked in 2005 with a series of controversies surrounding Buddhist and monarchic institutions, and the army dissolved Thaksin's party with a coup d'état in 2006 and banned over a hundred of its executives from politics. After the coup, a military government was installed for one year.

The military government faced significant resistance, with protesters frequently storming government buildings and elements within the military threatening yet another coup. In 2007, a civilian government led by the Thaksin-aligned People's Power Party (PPP) was elected. Another protest led by PAD ended with the dissolution of PPP, and the Democrat Party led a coalition government in its place. The pro-Thaksin United Front for Democracy Against Dictatorship (UDD) protested both in 2009 and in 2010, the latter ending with a violent military crackdown causing more than 70 civilian deaths.

After the general election of 2011, the populist Pheu Thai Party won a majority. Yingluck Shinawatra, Thaksin's younger sister, became prime minister. The People's Democratic Reform Committee organised another anti-Shinawatra protest after the ruling party proposed an amnesty bill which would benefit Thaksin. Yingluck dissolved Parliament, and a general election was scheduled, but her decision was invalidated by the Constitutional Court. The political crisis ended with another coup d'état in 2014.

The ensuing National Council for Peace and Order, a military junta led by General Prayut Chan-o-cha, led the country until 2019. Civil and political rights were restricted, and the country saw a surge in lèse-majesté cases. Political opponents and dissenters were sent to "attitude adjustment" camps; this was described by academics as indicating the return of fascism to Thailand. Bhumibol, the longest-reigning Thai king, died in 2016, and his son Vajiralongkorn ascended to the throne. The referendum and adoption of Thailand's current constitution happened under the junta's rule. The junta bound future governments to a 20-year national strategy 'road map' it laid down, effectively locking the country into military-guided democracy.

In 2019, the junta agreed to schedule a general election. General Prayut continued his premiership with the support of an elected Palang Pracharath Party coalition in the House and junta-appointed Senate, despite allegations of election fraud. An extended two-year period of pro-democracy protests were subsequently triggered by distrust in the election as well as increasing royal prerogative, democratic and economic regression under monarchy-supported military rule, retaliatory dissolution of the pro-democracy Future Forward Party, regressive policies on political issues like women's and labour rights, forced disappearances and deaths of political activists like Wanchalearm Satsaksit, and various political corruption scandals including 1MDB. The protests brought forward unprecedented demands to reform the monarchy and the highest sense of republicanism in the country's history.

Thailand's reformist opposition – the progressive Move Forward Party and the Pheu Thai Party – won the 2023 general election, ending 9 years of royalist-military rule under Prayut. Srettha Thavisin of the Pheu Thai Party became prime minister, while Thaksin Shinawatra returned after years in self-imposed exile from the military regime. Thavisin was dismissed on 14 August 2024 by the Constitutional Court for "gross ethics violations". He was succeeded by Thaksin's daughter Paetongtarn Shinawatra, who spent a year in office before the Constitutional Court ordered her removal over a controversial phone call with Cambodia's president. The Court then ordered the arrest of Thaksin in September 2025.

In July 2025, violent clashes broke out between Thailand and Cambodia along their disputed border. On 27 December 2025, both countries mutually agreed to a ceasefire. Anutin Charnvirakul was elected Prime Minister in September 2025. On 12 December 2025, Anutin dissolved the House of Representatives. The 2026 election resulted in Anutin's Bhumjaithai Party winning the most seats in the House of Representatives, an electoral revival for Thai conservatism.

Totalling 513,120 square kilometres (198,120 sq mi), Thailand is the 50th-largest country by total area. Thailand comprises several distinct geographic regions, partly corresponding to the provincial groups. The north of the country is the mountainous area of the Thai highlands, with the highest point being Doi Inthanon in the Thanon Thong Chai Range at 2,565 metres (8,415 ft) above sea level. The northeast, Isan, consists of the Khorat Plateau, bordered to the east by the Mekong River. The centre of the country is dominated by the predominantly flat Chao Phraya River valley, which runs into the Gulf of Thailand. Southern Thailand consists of the narrow Kra Isthmus that widens into the Malay Peninsula.

The Chao Phraya and the Mekong River are the indispensable water courses of rural Thailand. Industrial scale production of crops use both rivers and their tributaries. The Gulf of Thailand covers 320,000 square kilometres (124,000 sq mi) and is fed by the Chao Phraya, Mae Klong, Bang Pakong, and Tapi Rivers. It contributes to the tourism sector owing to its clear shallow waters along the coasts in the southern region and the Kra Isthmus. The eastern shore has the kingdom's premier deepwater port in Sattahip and its busiest commercial port, Laem Chabang. Phuket, Krabi, Ranong, Phang Nga and Trang, and their islands, all lie along the coasts of the Andaman Sea and host luxurious resorts.

The climate is influenced by monsoon winds that have a seasonal character (the southwest and northeast monsoon). Most of the country is classified as Köppen's tropical savanna climate. The majority of the south, as well as the eastern tip, have a tropical monsoon climate. Parts of the south also have a tropical rainforest climate. A year in Thailand is divided into three seasons. The first is the rainy or southwest monsoon season (mid–May to mid–October), which is caused by southwestern wind from the Indian Ocean.

Rainfall is also contributed by Intertropical Convergence Zone and tropical cyclones, with August and September being the wettest period of the year. The country receives a mean annual rainfall of 1,200 to 1,600 mm (47 to 63 in). Winter or the northeast monsoon occurs from mid-October until mid-February. Most of Thailand experiences dry weather with mild temperatures. Summer or the pre-monsoon season runs from mid-February until mid-May.

Due to their inland position and latitude, the north, northeast, central and eastern parts of Thailand experience a long period of warm weather, where temperatures can reach up to 40 °C (104 °F) during March to May, in contrast to close to or below 0 °C (32 °F) in some areas in winter. Southern Thailand is characterised by mild weather year-round with less diurnal and seasonal variations in temperatures due to maritime influences. It receives abundant rainfall, particularly during October to November. Thailand is among the world's ten countries that are most exposed to climate change. In particular, it is highly vulnerable to rising sea levels and extreme weather events.

National parks in Thailand are defined as an area that contains natural resources of ecological importance or unique beauty, or flora and fauna of special importance. Protected areas include 156 national parks, 58 wildlife sanctuaries, 67 non-hunting areas, and 120 forest parks. They cover almost 31 per cent of the country. The parks are administered by the National Parks, Wildlife and Plant Conservation Department of the Ministry of Natural Resources and Environment. The Khao Kheow Open Zoo in Chonburi is the second largest zoo in Asia. The largest national park is Kaeng Krachan National Park.

Thailand has a mediocre but improving performance in the global Environmental Performance Index, with an overall ranking of 91 out of 180 countries in 2016. The environmental areas where Thailand performs worst (i.e., highest-ranking) are air quality (167), environmental effects of the agricultural industry (106), and the climate and energy sector (93), the later mainly because of a high CO2 emission per kWh produced. Thailand performs best (i.e., lowest-ranking) in water resource management (66), with some major improvements expected for the future, and sanitation (68). The country had a 2019 Forest Landscape Integrity Index mean score of 6.00/10, ranking it 88th globally out of 172 countries.

The population of elephants, the national symbol, has fallen from 100,000 in 1850 to an estimated 2,000. Poachers have long hunted elephants for ivory and hides, and now increasingly for meat. Young elephants are often captured for use in tourist attractions or as work animals, where there have been claims of mistreatment. In 1989, the government banned the use of elephants for logging, leading many elephant owners to move their domesticated animals to the tourism industry.

Poaching of protected species remains a major problem. Tigers, leopards, and other large cats are hunted for their pelts. Many are farmed or hunted for their meat, which supposedly has medicinal properties. Although such trade is illegal, the well-known Bangkok market Chatuchak is still known for the sale of endangered species. The practice of keeping wild animals as pets affects species such as Asiatic black bear, Malayan sun bear, white-handed lar, pileated gibbon, and binturong.

Prior to 1932, Thai kings were feudal or absolute monarchs. During Sukhothai Kingdom, the king was seen as a dharmaraja or 'king who rules in accordance with dharma'. The system of government was a network of tributaries ruled by local lords. Modern absolute monarchy and statehood was established by Chulalongkorn when he transformed the decentralised protectorate system into a unitary state. On 24 June 1932, Khana Ratsadon (People's Party) carried out a bloodless revolution which marked the beginning of constitutional monarchy.

Thailand has had 20 constitutions and charters since 1932, including the latest and current 2017 constitution. All constitutions state that the politics is conducted within the framework of a constitutional monarchy, but the de facto form of government has ranged from military dictatorship to electoral democracy. Thailand's current form of government is part democracy and part dictatorship; many terms are used to describe it. Thailand has had the fourth-most coups in the world. "Uniformed or ex-military men have led Thailand for 55 of the 83 years" between 1932 and 2009. Most recently, the military junta self-titled as the National Council for Peace and Order ruled the country between 2014 and 2019.

Government is separated into three branches:

The legislative branch: the National Assembly is composed of the Senate, the 200-member indirectly elected upper house and House of Representatives, the elected 500-member lower house. Its most recent election is the 2026 general election. A coalition led by the Bhumjaithai Party currently holds the majority. The 2024 Thai Senate election was the first senate election held under the current constitution in the process criticised as "the most complicated election in the world". The senate is allegedly dominated by Bhumjaithai Party-affiliated senators.

The executive branch consisting of the Prime Minister of Thailand, the head of government, and other cabinet members of up to 35 people. The prime minister is elected by the House of Representatives. The current constitution mandates that prime ministers are to be considered from candidates nominated by political parties before the election. The current prime minister is Anutin Charnvirakul, a member of the Bhumjaithai Party.

The judiciary is supposed to be independent of the executive and the legislative branches, although judicial rulings are suspected of being based on political considerations rather than on existing law.

Military and bureaucratic aristocrats fully controlled political parties between 1946 and the 1980s. Most parties in Thailand are short-lived. Between 1992 and 2006, Thailand had a two-party system. Later constitutions created a multi-party system where a single party cannot gain a majority in the house.

A hereditary monarch serves as head of state. The current King of Thailand is Vajiralongkorn (Rama X), who has reigned since October 2016. The powers of the king are limited by the constitution and he is primarily a symbolic figurehead. However, the monarch still occasionally intervenes in politics, as all constitutions pave the way for customary royal rulings. Some academics outside Thailand, including Duncan McCargo and Federico Ferrara, note extraconstitutional role of the monarch through a "network monarchy" behind the political scenes.

The monarchy is protected by the severe lèse majesté law, even though the people's attitude towards the institution varies from one reign to another. Lèse-majesté laws allow critics to be jailed for three to fifteen years. After the coup d'état in 2014, Thailand had the highest number of lèse-majesté prisoners in the nation's history. Human rights in Thailand has been rated not free on the Freedom House Index since 2014.

In 2024 the Constitutional Court banned the victors of the 2023 parliamentary elections, the Move Forward Party and all of its leaders from politics for its proposal to reform the lèse-majesté, arguing it posed a threat to the constitutional order. The Economist criticised the move as an example of "lawfare" and pointed to the dissolution of its predecessor party, Future Forward in 2020, as the latest example of how an "alliance of conservative forces in Thailand—including monarchists, the army and a handful of business tycoons—has sought to suppress opposition".

On the Freedom in the World 2024 Report, the status improved from not free to partly free due to competitive parliamentary elections and the formation of a new governing coalition by what had been a major opposition party, though unelected senators ensured that the party with the most votes was excluded.