Question

What communist gains around the world created the fear that set the stage for the excesses of mccarthyism answers?

Answer 1

communism in China, Soviet nuclear bombs, and discovery of Soviet agents in the United States

Answer 2

The red scare  that lay the ground for
mccarthyism was sparked off by numerous success stories of the communist forces.
The success of communism forces in china, and the increased mentions of soviet nuclear bombs and the discovery of several agents from USSR in the USA territory led to red scare that reached its peak with the sputnik news.