Final answer:
The Red Scare was caused by the USSR turning to communism in the 20th century.
Step-by-step explanation:
The correct answer is USSR. The Red Scare was a period of anti-communist hysteria that occurred in the United States during the early 20th century. It was a response to the fear that communism, as represented by the Soviet Union (USSR), would spread and threaten American democracy. The Red Scare led to widespread paranoia, government investigations, and the suppression of political dissent.
Learn more about The Red Scare and communism in the 20th century