Khmer:

 

The Khmer empire rose in what is modern day Cambodia. It was the most powerful civilization on the mainland at this time. They started conquering other kingdoms near them. They reached the their highest peak around 1200. They started farming lots of rice and they made incredible irrigation systems. This made it possible to grow 3 to 4 crops a year which tripled or quadrupled the harvests. Their capital city was named Angkor Wat which was a very elaborately built city with temples, complexes and an observatory.(Perry)