History of Thailand is divided into 5 periods:
Ancient Period (pre-Sukhothai era)
Sukhothai Period (1238 – 1349)
Ayutthaya Period (1350 – 1766)
Thonburi Period (1767 – 1781)
Bangkok Period (1782 – Present)
It is generally believed that the Thai people originated from the Tai people who migrated from Southern China around 800 CE. Around this time, the legendary Tai chief, Simhanavati, founded the city of Chiang Saen located in the northern part of what is now the province of Chiang Rai. During his reign, the Tais made contact with the Indianized states of southern Asia. From them, Theravada Buddhism and Sanskrit words were adopted as part of the local culture. This was also the period when Dharavati principalities were founded in the north. Modern research however reveals that Dhavarati culture existed even in the 4th century CE. In fact, ancient documents show that a certain Haripunchai Kingdom, centered in the present province of Lamphun, was founded by a hermit named Suthep as early as 629 AD.
Towards the end of 12th century, many principalities were overrun by the Khmer Empire. However, in the beginning of the 13th century, Haripunchai Kingdom flourished with the building of many temples. During this time, the Lan Na Kingdom emerged as supreme in the northern part of present day Thailand. It was centered in the present province of Chiang Mai.
Around the middle of the 13th century, the Kingdom of Sukhothai became the chief rival of the Lan Na Kingdom. It was established by Sri Indraditya but it was during the reign of King Ram Khamheng that the kingdom achieved its true greatness. This king is believed to have created the Thai Alphabet.
In 1350, Phra Chao U-thong established the Ayutthaya Kingdom. Its government was absolute monarchy patterned after the Khmer which regarded the king as god-like with unquestioned authority. The kingdom became a colony of Burma for 15 years until King Naresuan of Phitsanulok, overthrew them. In 1767, the Burmese returned and this time, they completely ruined the Ayutthaya Kingdom.
Yet, the commander-in-chief of the Thai army escaped and established his own kingdom. His name is King Phra Chao Taksin. He made Thonburi, located west of the Chao Praya River, across the present old part of Bangkok, his capital. For 15 years, he reigned over a kingdom who was in constant warfare with the Burmese in the north, the Khmer in the east, and the Malay states in the south. In 1782, he died when his own soldiers executed him.
The capital of Siam was moved to Bangkok by King Yodfa Chulaloke, King Rama I of the Chakri Dynasty. To date, the dynasty has had 10 kings including the present King Maha Vajiralongkorn.
On June 24, 1932 during the reign of King Rama VII or King Chaoyuhua, the system of government was changed from absolute monarchy to constitutional monarchy with the prime minister as the head of government and the king as head of state. The change occurred when a coup d’état succeeded in establishing a new government with most of the king’s powers removed under Thailand’s first constitution. This is called the 1932 Siamese Revolution, a turning point in Thai History. In 1939, Siam was officially changed to Thailand as the name of the country.