Question

Why was there a fear of communism and communist subversion after World War II?

Answer 1

The threat was real. The Soviets didn't demilitarize like the allies did. They kept domination of the lands they "liberated".
Add to that the inconceivable power of the nuclear devices that we used to end the war. Americans just start to come to grips with that when the learn that Americans helped the Soviets get the same weapon. The Rosenbergs not only betrayed their country they got every one thinking about the possibility that there could be other spies.
Joe McCarthy fed off the real concerns of Americans when he started his wild accusations about Communist infiltration. Yes, he made up most of it and ruined careers with his committee hearings, but the fear was there to start with.
Throw in the Soviet space program. Sputnik circling the Earth was enough to get anybody worried. Who nows what that thing can do?
The people who built bomb shelters didn't help much. They profited by selling underground shelters and increased fear as they did.

Answer 2

Thanks. I appreciate it.

Answer 3

:)