Why did a ""red scare"" sweep the united states after the end of world war ii?

The red scare emerged after the end of world war II because the Soviet Union became a powerful country, powerful enough to challenge the U. S. position as the hegemon of the world.

Explanation:

The Soviet Union dominated most of Eastern European countries, had industrialized, and was promoting communism around the globe. In the U. S., many government officials, especially senator Joseph McCarthy, feared that the Soviet may do the same in the United States.

This red scare caused a series of acts of espionage, trials, and persecutions against perceived communists in the United States.