Answer:
A
Explanation:
After WWII, the Cold War began between the United States and the Soviet Union. The main reason for this war was the difference between communism and capitalism. A couple theories arose during this time period, one of which was the Domino Theory. The Domino theory stated that if one country "fell" to communism, others around it would fall as well. The United States joined the war in Vietnam in order to stop the spread of Communism.
