Cambodia, Laos, and Indonesia
From India, Buddhism spread to the East and South.
Cambodia was influenced by India early in its history, and Mahayana Buddhism took a foothold with its people. Early Cambodian history is not well documented, so it is not until the ninth century that we know Buddhism was being practiced there. Kings of the Khmer, who were dominate in Cambodia, started to build large temples and monasteries.
Then at the turn of the twelfth century, King Jayavarman VII came into power. He was a devout Buddhist, and Mahayana Buddhism became the dominant religion of the kingdom under his influence. Neighboring Thailand was soon to have a strong effect, however, and by the end of the thirteenth century Theravada was predominant.
Buddhism has exerted influence on Southeast Asia since the first century
When Pol Pot and the Khmer Rouge communists took control of Cambodia in the 1970s, they tried to eradicate Buddhism and nearly succeeded. There were 65,000 monks in the Sangha before 1970, and after Pol Pot, that number was reduced to 3,000. Approximately two-thirds of the Buddhist temples were destroyed. Today Buddhism is attempting to re-establish itself but political unrest continues. There has been resurgence in the sangha, and 95 percent of the population is Theravada Buddhist.
As in Cambodia, Laotian Buddhism was probably introduced by the Khmer. Later, it was heavily influenced by Thailand and thusly became Buddhist in the Theravada school. Communists also tried to rid Laos of Buddhism in 1975, and a large percentage of the sangha fled the country. The remaining religious communities were under strict state control. Recent reforms and dialogues are moving to declare Theravada Buddhism the state religion. Fully 60 percent of the population is considered to be practicing Buddhists.
The first Buddhists arrived in Indonesia sometime in the first century