The correct answer is "Expansion of Soviet influence."
After World War II, the United States and Soviet Union emerged as global superpowers. Both countries tried to expand their beliefs and ideas to other countries. The US promoted capitalism and democracy while the Soviet Union promoted communism. The US fundamentally disagreed with communism and believed it was a terrible system that limited the individual freedoms of citizens.
To stop communism from spreading, the federal government adopted the policy of containment. This was made to stop the spread of communism and the power/influence of the Soviet Union, especially in the Eastern hemisphere.