In 1950 a confluence of events occurred that caused the anti-communist fervor not only in the U.S, but also in western Europe as well as Britain. Mao Zedong, after nearly 25 years defeated Chiang Kai-shek making the entire nation Communist. Russia exploded it's first atomic bomb with secrets provided by the American and British traitors (Ethel and Julius Rosenberg in the U.S. and Klaus Fuchs in England). Russia dominated eastern Europe and forcefully put down an uprising in Budapest in 1956 whose roots are traced to around 1950. Ho Chi Minh began his offensive against French troops in Indo China in January of 1950, supported by Russia. On June 25, 1950, North Korea invaded South Korea. North Korea's army and air force were totally supplied by Russia and thousands of Russian advisors participated.
In war weary Europe and Britain, rebuilding following WW II was finally beginning in earnest.
Russia blockaded West Berlin, hoping to force the western powers to accede to its demands to retreat from the city... the Berlin Airlift broke the blockade finally.
So... who stood between communist domination by the massive land and air forces of Russia, now armed with atomic bombs? The U.S. aided by Britain. The specter of communist domination of a world recently rid of the Axis powers certainly did percipitate excesses by Senator McCarthy and others... but considering everything that was happening, it was fairly shortlived and McCarthy was censured.
The threat wasn't just to "their Capitalist system"... but to the entire western world... By the way, I think Vietnam is communist today, no?