One of the world empire in 802CE to 1431 is Khmer Empire which was the largest and powerful state in Southeast Asia, based in what is now Cambodia. The main religions were Hinduism and Buddhism. Angkor was the capital of the Khmer Empire and believed to have been one of the largest cities in the world at the time, with a population of one million.
At its peak, the Khmer Empire controlled most of Southeast Asia, including the current areas of Cambodia, Laos, southern Vietnam, and Thailand along the Mekong River, the world’s seventh longest river.
The empire’s decline started with the revolt from the area of Thailand who started forming their kingdoms and the Mongols, who were invading multiple arenas. The Khmer also had problems with their water system when it became filled with silt as trees were cut down to make rice fields and flood control was compromised. By 1431 a Thai kingdom took control of Angkor and ended the Khmer empire.
Population: 1 million
Size: 1 million Km2
During: 802CE to 1431
Current country: Cambodia or Khmer
Formation and growth under king:
Yasodharapura --- the first of Angkor
Jayavarman II --- the founder of Angkor
Golden age of Khmer Civilization
Suryavarman II --- Angkor Wat
Jayavarman VII --- Angkor Thom
Jayavarman VIII --- the last blooming