The Chenla people, also called the Kambuja (or Cambodian in the modern form of the word), from the mountains of Laos invade and overthrow the Phnom empire around 550 AD. The Cambodians are united into the first Khmer kingdom by king Jayavarman I, 657-695, with his capital at Isanapura. Their expansion is stopped after 700 AD by an invasion from Java.

The Hindu Mons people, ethnically related to the Khmer, establish the kingdom of Dvaravati in northern Thailand around 450 AD. Dvaravati becomes part of the Khmer empire by 700 AD.

Many Thai tribes migrate from the area around southern China and Vietnam west across the Mekong River. A number of minor kingdoms, under Khmer domination, are founded by 600 AD. One branch settles in Burma and becomes known as the Shans. The Lao people settle the mountainous region now called Laos. The area of modern Thailand is settled by the Siam people (Shan and Siam come from the same root word).