The Mon-Khmer and the Lawa people migrate throughout the region. The Mons and Khmers split up, with the Mons living mostly between the Salween and Irrawadi rivers, while the Khmers (ancient Cambodians) make their homeland on the lower Mekong River. The Lawas lived in and north of the Chao Phraya valley (now part of modern Thailand).

Many Brahmins, the caste or class of priests in the Hindu religion, migrated to southeast Asia, where they settled down, engaged in trade and intermarried with the natives. Their descendants became important in the government of the many kingdoms which arose, such as Phnom, Dvaravati, Chenla (Khmer), Champa, Srikasetra, Suddhammati, and Srivijaya.

By 100 AD, the Khmer people were united under the Phnom kingdom (B'iu Nam or Funan in Chinese). The founder according to Khmer oral history was an Indian Brahmin called Kaundinya. There was strong influence from both the Chinese and Indian cultures. Buddhism was introduced after 200 BC from the Indian Maurya empire.