Answer:
The era after the Second World War, was dominated by one fact: the conflict that arose between two powers, and their very different perception on how social, political, and economic affairs, should be handled. These were the USSR and the U.S. While the first embraced Communism, the other embraced Democracy and Capitalism. In the end, the result was, a world divided by these two ideologies, and two countries who dedicated themselves to make the other look like evil itself.
The era of McCarthyism in the 1950´s was no joke, and although he was not the first to initiate the panic in the U.S regarding the possible presence and influence of spies in the country, especially in the U.S Department of State, he for sure became a force that drove the panic forward.
Being a U.S Senator did add to the credibility that Joseph McCarthy enjoyed, and he used that power to go around telling people that he had evidence, list of names supposedly, that Communists had infiltrated the U.S Department of State, and other U.S government organizations, to spy on the U.S. Given that previously to McCarthy´s accusations, people like Alger Hiss, and Hollywood actors and actresses, had been tried and convicted for supposedly being Communist spies, and given that Americans were seeing the fast spread of Communist power in the world, they were more than ready to believe McCarthy´s accusations, even if he never produced actual evidence.
The result, nationwide panic, and a lot of persecution to people who were deemed Communist, but were never proven as spies.