Answer: The Answer is A.
Step-by-step explanation:
The reason why the Cold War started was because the U.S. was afraid of Eastern Europe, since it was mostly made of communist countries. The Soviet Union was afraid of Western Europe, which had many NATO countries in it. The Berlin Wall was built during the Cold War, because the Soviet Union didn’t want East Berliners going to West Berlin, and the Red Scare happened before World War 2, which was before the Cold War. The US invasion of South Korea happened after NATO was established, and NATO was made because of the Soviet Union.