Which modern-day nations occupy much of the territory of the Khmer Empire?

Modern-day nations that occupy much of the territory of the Khmer Empire are Cambodia and Thailand, with smaller areas of it being in Vietnam, Laos, and China.

Explanation:

The Khmer Empire was a well-developed empire that was located in the mainland part of Southeast Asia. It was the dominant force in the region for several hundred years, and it managed to achieve multiple great things. This empire, at its peak, was so powerful that it managed to defeat the Mongols and stop their expansion in the region, even though the Mongols were very close to their base and were at the height of their power.

The majority of the territory of the Khmer Empire was located on the territories of modern-day Thailand and Cambodia, being spread on almost all of their territories. It was not just these two though, but the southern part of Vietnam, what is now the border area of Laos with Thailand, and even a little bit of southern China, were part of this great empire.