The origins of Thailand are related to the migration of Thais from the southwestern part of China.

An excerpt from the article 31 facts about Thailand

This population reached the territory of present-day Thailand in the 10th-12th centuries. The Thais settled in the Chao Phraya basin, and assimilated with the Khmer people living there, from whom they took over their culture and religion - Buddhism.

In 1350, they established their capital in the Chao Phraya Valley - Ayutthaya, and soon this country covered the entire Indochinese Peninsula.

The state flourished in the 15th century, and in the 16th and 17th centuries, there were first contacts with Europeans (Portuguese, Spanish, Dutch, and English).