Most Thais (approximately 95%) believe in a form of Buddhism called Theravada. This Theravada school of Buddhism prevails in Burm, Ceylon, Cambodia and Laos as well as Thailand.Buddhism has been combined with folk beliefs and ancestor worship, as well as aspects of Chinese religions that many Thai-Chinese still adhere to. The Buddhist architecture is similar to that of surrounding countries, especially Cambodia and Laos, because they share common cultural and historical heritage.
Buddhism is a religious movement started in the sixth century B.C. by Prince Siddhartha Gutama Sakyamuni. Later, he became known as the prophet, Buddha. He encouraged his followers to follow the Middle Way and practice moderation in all aspects of living. Buddha taught that life was pain and suffering because we have cravings and desires. He saw that the only end to the suffering was when those cravings and desires ceased to exist. When the end of suffering was achieved, one had reached nirvana. This state of absence of craving and by extension suffering, is also known as enlightenment.
In the next few centuries, Buddhism spread throughout Asia. Buddha’s teachings were interpreted differently by different groups and resulted in several sects including Theravada Buddhism. In Ceylon, present-day Sri Lanka, the teachings were put into written form in Pali (an Indo-Aryan language realted to Sanskrit). These teachings from the Theravada school of Buddhism were imported to Thailand around the sixth century A.D. and became the state religion during the Thai kingdom of Sukothai is the thirteenth century A.D.
Other forms of Buddhism reached Thailand at different periods in Thai history. Theravada Buddhism is thought to be the first. Next was the Mahayana school of Buddhism that spread from India to Sumatra, Java and Kambuja (Cambodia) starting in the fifth century A.D. This form of Buddhism is more evident in the south of Thailand and is believed to have been at its height when Thailand was part of the Suryavarman dynasty in Cambodia. For awhile, Theravada and Mahayana both existed in Thailand, but Theravada already had a large following and Mahayana never eclipsed it in popularity.
In 1057 A.D., Burma’s borders extended into areas of modern-day Thailand, including Chiangmai, Lopburi and Nakon Pathom. At the time, Buddhism in India was declining and the Theravada Buddhism common in Burma at the time altered from its original form. This type of Buddhism became known as Burma Buddhism.
The last form of Buddhism introduced to Thailand was called Ceylon (Lankavamsa) Buddhism. Around 1153 A.D. there was a powerful king of Ceylon that was a strong supporter of Theravada Buddhism. Buddhist monks from neighboring countries, like Burma, Kambuja, Lanna (Northern Thailand), Pegu (Lower Burma), and Lanchang (Laos) migrated to Ceylon in order to learn the form of Dhamma practiced there. Some Ceylonese monks returned with the local monks and settled in Nakon Sri Thammarat in the south of Thailand. Many kings from the Sukothai and Ayudhaya Period supported Ceylon Buddhism.
Today, Thailand is called a Theravada Buddhist country, although there are a few Mahayan monks and monasteries that have a Chinese influence. The various forms of Buddhism in Thailand have never competed with each other and seemed to blend gracefully with each other, influencing the beliefs of different regions of Thailand to different degrees.