However, the Thai history has been changed by the archaeological excavations in the village of Ban Chiang in the Nong Han District of Udon Thani province in the Northeast. From the evidence of bronze metallurgy, it now appears that the Thais might have originated here in Thailand and later scattered to various parts of Asia, including China.

The controversy over the origin of the Thais shows no sign of definite conclusion as many more theories have been put forward and some even go further to say that Thais were originally of Austronesian rather than Mongoloid. What the outcomes of the dispute may be, by the 13th century the Thais had already settled down within the southeast Asia.

From the 9th to the 11th century, the central and western area of Thailand was occupied by Mon civilization called Dvaravati. The Mon share the same common lineage as the Khmers and settle in southern Burma latter. The Influence of Dvaravati include Nakhon Pathom, Khu Bua, Phong Tuk , and Lawo (Lopburi). Dvaravati was Indianized culture, Theravada Buddhism was remained the major religion in this area.

By the 11th-12th centuries, Mon Influenced over central Thailand. Khmer cultural influence was brought in the form of language, art and religion. The "Sanskrit" language was entered in Mon-Thai vocabulary during the Khmer or Lopburi Period. The influence of this period has affected many provinces in the north-east such as Kanchanaburi and Lopburi. The Architecture in "Angkor" was also constructed according to the Khmers style. The Khmer built stone temples in the northeast, some of which have been restored to their former glory, those at Phimai and Phanom Rung and further cultures are stone sculptures and stone Buddha images. Politically, however, the Khmer cultural dominance did not control the whole area but power through vassals and governors.

Lan Na flourished for over 200 years. Its arts and literature rose at the peak, especially in the middle of 15th century, the King Tilokoraj period. Chiang Mai in this period was also chosen as the navel of the eight world synod of Theravada Buddhism.

After the death of King Tilokoraj, the kingdom suffered from internal conflicts. Lan Na weakened because of wars with Sukhothai's successors.

During this time Thai had strong friendship with neighboring countries. It absorbed elements of various civilizations which they came into contact. Thai maintained and advanced their culture with China. The potters entered Thai artistry and extensive trade was established with Cambodia and India.

After the death of Khun Pha Muang in 1279, Ramkhamhaeng King, the third son of Si Inthrahit, ascended to the throne. Under the Ramkhamhaeng King, Sukhothai had strong friendship with neighboring China. Ramkhamhaeng King organized a writing system which became the basis for writing and eventually developed to be the modern Thai alphabet.

King U-Thong and his immediate successors expanded Ayutthaya's territory, especially northward towards Sukhothai and eastward towards the Khmer capital of Angkor. The greater size of government could not remain the same as during the days of King Ramkhamhaeng. The society during the Ayutthaya period was strictly hierarchical. There were, roughly, three classes of people king at the top of scale. At the bottom of social scale were commoners and the slaves.

In the early 16th century, the European visited Ayutthaya, and a Portuguese embassy was established in 1511. Portugal's powerful neighbor Spain was the next European nation to arrive in Ayutthaya forward the end of the 16th century. In he early 17th century they saw the arrival of two northern European, the Dutch and the British, and France in 1662.

In the mid-16th century, Ayutthaya and the independent kingdom in Chiang Mai was put under the control of the Burmese, but Thais could regain both of the capitals by the end of the century.

The Burmese invaded Ayutthaya again in 1765. This time Burmese caused much fear to Thais. Burmase soldiers destroyed everything, including temples, manuscripts, and religious sculpture. After the capital fell in their hands for two years, the Burmese effectiveness could not further hold the kingdom. Phaya Taksin, a Thai general, promoted himself to be the king in 1769. He ruled the new capital of Thonburi on the bank of Chao Phraya River, opposite Bangkok. Thais regained control of their country and thus scattered themselves to the provinces in the north and central part of Thailand. Taksin eventually turn himself to be the next Buddha and was dismissed and executed by his ministers who did not approve his religious values.

In 1809, Rama II or King Buddha Loet Lad, son of Rama I took the throne until 1824. He devoted himself to preserve the Thai literature that had remained from Ayutthaya period and produced a new version of Ramakien or Thai Ramayana, the classical literature.

In 1824-1851, Rama III or King Nang Klao was successful in re-establishing relation and making trades with China which was necessary to meet the increasing domestic agricultural production.

Rama IV or King Mongkut (Phra Chom Klao), who reigned from 1851 to 1868 lived as a Buddhist monk for 27 years. During his monastic period, he could speak many languages such as Latin, English, and five other languages. He also studied western sciences and adopted the discipline of local Mon monk. Under his reign, he created new laws to improve the women's and children's right, opened new waterways and roads, and created the first printing press.

Rama V or King Chulalongkorn, Rama IV's son, continued the throne from 1868 to 1910. He started to reform the tradition, legal and administrative realm by allowing officials to sit on chairs during royal audiences. Under the reign of Rama V, Thailand developed relations with European nations and the USA. He introduced schools, roads, railways, and Thailand's first post office. He even established civil service system. In 1892, Rama V overhauled the administration of Siam to a form of cabinet government with 12 ministers.

In 1886, Siam lost some territory to French, Laos and British Burma accorded the foreign powers intercede. After that King Chulalongkorn declared Thailand as an independent kingdom on the 23rd of October, making this day as a national holiday. Every year this national holiday is celebrated in commemoration of this event and people lay wreaths in memory of king they called "Phra Piya Maharaj"

Rama VI or King Vajiravudh, took the throne from 1910 to 1925. During his short reign, he introduced the westernization to Thailand. He introduced the primary school education, Thai women were encouraged to grow their hair at a certain length. Surnames were introduced, and football was introduced in Thailand.

1925-1935 was the period of Rama VII or King Prachadhipok, Rama VI's brother. He changed Siam's form of government from absolute monarchy to democracy. This revolution developed the constitutional monarchy along British lines, with mixed military and civilian group in power. At that time, Phibul Songkhram was a key military leader in the 1932 coup. He maintained his position and power from 1938 until the end of World War II.

Rama VIII or King Ananda Mahidol, a nephew of Rama VII, took the throne in 1935 but was assassinated under mysterious circumstances in 1946. His brother King Bhumipol Aduldej succeeded as Rama IX.

Under Rama IX's government, the country's name was officially changed from "Siam" to "Thailand" in 1946 which was defined in Thai as "Prathet Thai", the word "Prathet" means "country" and the word "Thai" means "free" referring to the Thai races.

In 1946, King Ananda Mahidol (Rama VIII) who had returned from Switzerland after completing his education was assassinated with a pistol. Seni and Kukrit (Seni's brother) were unseated in a general election and a democratic civilian group took power for a short time because Phibul returned to overthrown in 1948.

In 1951, Phibul's power was snatched by General Sarit Thanarat, who continued the tradition of military dictatorship. However, Phibul still retained the premier until 1957 but finally exiled by Sarit. Sarit was forced to resign by the general election. He escaped abroad after the election and returned in 1958 to launch another coup. By that time he expanded his power to the constitution by dissolving the parliament and banning all political parties until his death from cirrhosis in 1963.

During Vietnam War from 1964 to 1973, Thailand was based for USA operations with the permission of army officers, Thanom Kittikachorn and Praphat Charusathien. Bangkok was the center for troop rest and recreation. As a reaction to political repression, Thai students demanded the real constitution in June 1973. In October of the same year, students from Thammasat University in Bangkok went to the streets demanding a new constitution but "King Bhumiphol (Rama IX) and General Krit Sivara tried to mediate to prevent the bloodshed confrontation, forcing army leader, Thanom and Praphat to leave Thailand by helicopters. In 1974, a new constitution was declared by a civil government under the leading of Prof. Sanya Dharmasakti but it didn't last for a long time.

In 1976, Thammasat University once again became the battlefield. Students demonstrated to protect the return of Thanom as a monk and Thanin Kraivichien, a new right-wing government official was declared as a premier. This incident made Thai students and numerous idealists joined the insurgents in the forest. Finally Thanin was forced to resign by another coup in 1977. In 1980, the military position changed again, leaving General Prem Tinsulanonda at the helm. Prem retained as primer until 1988 who was politically credited for the economic stabilization of Thailand in the Vietnam post-war years.

During the latest period of democracy (1988-1991), Chatichai Choonhaven led a coalition of parties. The economy had unprecedented boom for three years. However, Chatichai was arrested by the soldiers who were ordered by the military to intervene as he was in the airport hangar because of corruption charges and the accusation of inability against him. Then the non-elected primer General Suchinda Kraprayoon appointed himself to hold the position on May 18, 1992. In one intervening incident, hundreds of pro-democracy protestors and many Thai people were killed and wounded in the violence. King Bhumipol (Rama IX) had to lend a hand to stop the bloodshed confrontation. Afterwards, Suchinda was forced to resign and Anan Panyarchun was appointed to the temporary primer at that time.