The correct answer is D. The main difference between the Vietnam War and the Korean War was that the Vietnam War resulted in an increase in territory for communist forces, but the Korean War did not.
The Vietnam War ended with a communist victory, where North Vietnam annexed the territories of South Vietnam, unifying them under the name of Socialist Republic of Vietnam.
The Korean War, on the other hand, resulted in a status quo ante bellum, with minimal territorial changes and without a clear victor. Therefore, North Korea, communist, and South Korea, capitalist, maintained their territories, a situation that remains until today.
