Answer:
This fear skyrocketed during World War I. As this war was ending, a fear-driven movement known as the first Red Scare began to spread across the United States. In 1917, Russia had undergone the Bolshevik Revolution. As a result of this event, that country tried to establish a communist government and withdrew its troops from the war effort. Americans believed that Russia had let down its allies, including the United States, by pulling out of the war. In addition, communism was, in theory, an expansionist ideology, spread through revolution. Many Americans feared that the communists in Russia, known as the Soviet Union following the Bolshevik Revolution, hoped to spread their ideology all over the world.