The historic period of Southeast Asia can, arguably, be dated from about the 3rd or 4th century ce, when an inscription, discovered at Vo Canh, Vietnam, was carved. The sociopolitical developments that occurred across Southeast Asia from this period through to the decline of the Khmer Empire in the 15th century are considerable. The early centuries of the 1st millennium saw the florescence of a number of cultures. Complex societies on the cusp of statehood arose from modern Myanmar, Thailand and Cambodia to the shores of Vietnam. A considerable amount of research has been undertaken on the earlier prehistoric societies of Southeast Asia, particularly in Thailand and Vietnam, but there is a lacuna in our understanding of the period that preceded the rise of the complex state in the region. Although the Vo Canh inscription may officially mark the beginning of the historic period in Southeast Asia, most of the information we have about the early 1st millennium ce comes from Chinese reports, histories and archaeological research.

Human colonisation of Southeast Asia has resulted in a huge range of ethnic and linguistic groups occupying different parts of the region. Gradually, the smaller groups are being subsumed into the more dominant cultures, but at least a dozen major language families still exist. Perhaps the most predominant language family is Thai, which is spread over a vast area of Southeast Asia, although its speakers have inhabited the country known as Thailand for only about a thousand years. Cambodia is dominated by Khmer-speakers, who have inhabited the area for at least two thousand years. Khmer is also widely spoken in the Truong Son uplands. This language was, at one time, spoken far into the Mekong Delta, an area now predominantly Vietnamese, as is all of the coastal area of Vietnam, where Cham was once widely spoken. Languages belonging to the Burmese, Karen and Mon families are spoken in Myanmar and western Thailand, and Chinese is spoken all over the region by ethnic Chinese migrants.