From the 5th to the 13th centuries, South-East Asia saw a series of powerful states which were extremely active in the promotion of Buddhism and Buddhist art alongside Hinduism. The main Buddhist influence now came directly by sea from the Indian subcontinent, so that these empires essentially followed the Mahāyāna faith. Examples include mainland kingdoms like Funan, the Khmer Empire and the Thai kingdom of Sukhothai as well as Island kingdoms like the Kalingga Kingdom, the Srivijaya Empire, Medang Kingdom and Majapahit.

Buddhist monks traveled to China from the kingdom of Funan in the 5th century CE, bringing Mahayana texts, a sign that the religion was already established in the region by this point. Mahayana Buddhism and Hinduism were the main religions of the Khmer Empire (802–1431), a state that dominated most of the South-East Asian peninsula during its time. Under the Khmer, numerous temples, both Hindu and Buddhist, were built in Cambodia and in neighboring Thailand. One of the greatest Khmer kings, Jayavarman VII (1181–1219), built large Mahāyāna Buddhist structures at Bayon and Angkor Thom.

In the Indonesian island of Java, Indianized kingdoms like the Kalingga Kingdom (6–7th centuries) were destinations for Chinese monks seeking out Buddhist texts. The Malay Srivijaya (650–1377), a maritime empire centered on the island of Sumatra, adopted Mahāyāna and Vajrayāna Buddhism and spread Buddhism to Java, Malaya and other regions they conquered.