McCarthyism was a movement started and perpetuated by US Senator Joseph McCarthy of Wisconsin in the 1950s. The senator was strongly opposed to the spread of communism throughout the world, and as a result, he started investigating people in the US for possible communist ties. In the eyes of many people, these investigations went too far by violating people’s rights to free speech and often ruining their lives by publicly tarnishing their reputations. Senator McCarthy was eventually censured by the body of the Senate for abusing his powers. As time went on, it was proven that some of the people McCarthy investigated actually were foreign spies, but there were also many totally innocent people subjected to his interrogations.
A fear of communism spread during the 1950s, partially because of several cases where communists groups rose to power in several different countries. Many people feared that this could happen in the US, and some were concerned that high-ranking government officials might already be secret communists waiting for an opportunity to use their power to aid a foreign enemy.
McCarthy used his power to help stoke the fires of these fears, and he eventually started publicly investigating people. Some were just regular middle-class citizens, but he also investigated a lot of high-profile people, including many in Hollywood. There were many reasons why McCarthy chose who he did — sometimes he had actual evidence against them, but in many cases, people were simply involved in organizations that he considered subversive, or they were acquaintances of someone else he was investigating.
People targeted during the era often found it difficult to find employment afterward. This was often the case even if they were eventually acquitted of any guilt. In part, this was because of the fear that any association with someone who had been investigated might make an individual or company look suspicious.
Eventually, evidence came to light that McCarthy had targeted some people as a way for him to exert influence. For example, he allegedly focused on some US Army officers as a way to threaten them into favoring draftees who were closely acquainted with certain senators. This is the kind of evidence that was in many ways responsible for McCarthy's downfall. Over time, the term "McCarthyism" has been used to describe any kind of movement where people use rumor and innuendo to publicly attack individuals for a belief or political leaning.