The term Indochina (originally Indo-China) was coined in the early nineteenth century, emphasizing the historical cultural influence of Indian and Chinese civilizations on the area.

The adjacent Malesian Region covers the Maritime Southeast Asian countries, and straddles the Indomalayan and Australasian realms.

It contains several mountain ranges extending from the Tibetan Plateau in the north, interspersed with lowlands largely drained by three major river systems running in a north–south direction: the Irrawaddy (serving Myanmar), the Chao Phraya (in Thailand), and the Mekong (flowing through Northeastern Thailand, Laos, Cambodia and Vietnam).

[citation needed] The countries of mainland Southeast Asia received cultural influence from both India and China to varying degrees.

[citation needed] Overall, Mainland Southeast Asia is predominantly Buddhist[11][12][13][14][15][16] with minority Muslim and Hindu populations.