Question

How did General MacArthur misjudge the Chinese during the Korean War?

Answer 1

He thought that the Chinese would not intervene in the Korean War. They did and effectively.

Explanation:

MacArthur, having routed the North Korean Army with the landings at Inchon, wanted to continue to the Chinese border and beyond. He thought the Chinese would not be able to resist Western forces.
He thought it would be a way to fight Communism. The Chinese Communists had recently completed a destructive Civil War and would not be able to resist the mechanized troops of the west.

The Chinese were able to attack with very large numbers and use infantry weapons, mortars and effective tactics to overwhelm the United Nations troops. The Korean war ended in a stalemate.