Answer:
Irrawaddy river
Step-by-step explanation:
The Kingdom of Pagan was the first kingdom to unify the regions of Burma (Myanmar). This kingdom settled in the region of the Irrawaddy river basin and its periphery laid the foundation for the rise of Burmese culture, the spread of the Burmese ethnic group in Upper Burma, and the growth of Buddhism in Southeast Asia. The kingdom collapsed in 1287 due to the Mongol invasions.