Thais migrate from southern China to present Thailand.
King Mengrai the Great founds a prosperous Buddhist society in northern Thailand. Further south, King Ramkamhaeng the Great establishes Sukhothai, eventually expanding into parts of what are now Laos, Myanmar (Burma), Cambodia and Malaysia.
King Narai welcomes foreign diplomats, traders and missionaries who are astonished at the size and opulence of his capital Ayutthaya.
The Burmese capture and loot Ayutthaya in 1767. A new capital is founded at Thom Buri, across the river from what is now Bangkok. King Rama I establishes a new capital in 1782, called Krungthep (“City of Angels”); foreigners name it Bangkok.
King Rama III reopens Siam to foreign influences. King Mongkut (Rama IV), fictionalized in The King and I, sends diplomats to England and France and offers Abraham Lincoln a pair of elephants to help fight the Civil War. Mongkut’s son, Rama V, abolishes slavery and establishes schools, a museum, a national library, and Siam’s first post office.
In 1917, Cambridge-educated Rama VI sends Thai troops to join the Allies in France in World War I. He also decrees that all Thais take a surname. Rama VII has a summer palace built at Hua Hin in the 1920s. Constitutional monarchy is imposed on the king, last of the absolute rulers, in 1932.
Hoping to gain lost territory, Thailand signs friendship treaties with Japan in 1940 and enters World War II on Axis side. Home front experiences arouse mixed emotions. After the war, the Allies invite Thailand to join the United Nations. Thailand prospers, its economy takes off, mainly because of tourism in the 1980s. Despite occasional military coups, democracy holds firm, thanks to a widely respected royal family.
Look more here:
Thailand Travel Guide