Question

One of the reasons for direct U.S. military involvement in the Vietnam War was the domino theory. How did this theory apply to Southeast Asia?

Both China and the Soviet Union wanted to install a communist regime in Vietnam.

If Vietnam became communist, China would rule Southeast Asia.

Without U.S. involvement in Vietnam, the Soviets would take over Southeast Asia.

If South Vietnam fell to communism, all of Southeast Asia would follow and fall to communism.