The term Red Scare has been retroactively applied to two distinct periods of strong anti-Communism in United States history: first from 1917 to 1920, and second from the late 1940s through the late 1950s. These periods were characterized by heightened suspicion of Communists and other radicals, and the fear of widespread infiltration of Communists in U.S. government.
In April 1919, a large-scale plot to mail thirty-six bombs to a variety of prominent Americans was uncovered. The intended recipients included immigration officials, Supreme Court Justice Oliver Wendell Holmes, the chairman of a Senate committee investigating Bolsheviks, Attorney General A. Mitchell Palmer, J. P. Morgan and John D. Rockefeller. On June 2 of the same year, bombs exploded in eight different cities within the same hour. One of the intended targets was again Attorney General Palmer, whose Washington, D.C. home was bombed. The man planting the bomb at Palmer's home was killed in the explosion, and evidence indicated that he was an Italian man living in Philadelphia.
This occurred during a time of heightened xenophobia in America. Various brands of radical anarchism were acquiring some notoriety, and their advocates were often recent immigrants to the U.S. The Industrial Workers of the World (IWW) was responsible for several prominent strikes in 1916 and 1917, and this too was seen as a threatening form of radicalism largely inspired by foreign born "agitators". By 1919, hundreds of strikes were occurring every month nation-wide, and the conservative press was commonly referring to strikes as "crimes against society," "conspiracies against the government," and "plots to establish communism.
As a result, even before the bomb plots of 1919, a series of immigration, anti-anarchist, and sedition laws (including the Sedition Act of 1918) were passed and widely exercised as a means to remove putatively undesirable elements from the country. In the words of David D. Cole, "the federal government consistently targeted alien radicals, deporting them[…] for their speech or associations, making little effort to distinguish true threats from ideological dissidents."
After the bombings, Attorney General Palmer initiated what came to be known as the Palmer Raids. These were a series of mass arrests and deportations of immigrants who were suspected of being leftists or radicals. A total of between 4,000 and 10,000 individuals were arrested over two years. Palmer placed J. Edgar Hoover, then 24 years old, in charge of this operation. At Hoover's specific direction, prisoners were questioned without access to attorneys and their bail was set prohibitively high. Many were beaten during their arrest or questioning.
The raids were initially highly praised by the public and press. The Washington Post proclaimed "There is no time to waste on hairsplitting over infringement of liberty," and the New York Times referred to the injuries inflicted on a group of suspects as "souvenirs of the new attitude of aggressiveness which had been assumed by the Federal agents against Reds and suspected Reds Eventually there was criticism of the raids. A group of twelve prominent lawyers that included future Supreme Court Justice Felix Frankfurter published "A Report on the Illegal Practices of The United States Department of Justice," citing violations of the Fourth, Fifth, Sixth, and Eighth Amendments to the Constitution and accusing Palmer of "illegal acts" and "wanton violence." Palmer then issued a series of warnings that a revolutionary plot to overthrow the government was to be launched on May 1, 1920. When the date passed without incident, Palmer was widely ridiculed. Adding to the criticism was the fact that evidence sufficient for deportation could be found for less than six hundred of the thousands who were arrested. In July 1920, Palmer's once-promising bid for presidential office was squelched when he failed to win the Democratic nomination.
As a result of the fear and oppression around the First Red Scare, membership in the Communist Party of the United States and similar Marxist/Communist groups was reduced by some 80 percent.
In 1919–1920, a number of states passed "criminal syndicalism" laws that made the advocacy of violence to secure social change unlawful. Traditional American ideals of free speech were restricted.
The Second Red Scare took place in the United States after World War II. It coincided with increased fears of espionage by Communists and heightened tension from Soviet oppression in Eastern Europe (beginning in 1946), the Berlin Blockade (1948–1949), Chinese Civil War (1949), and the Korean War (1950–1953). These fears spurred aggressive investigations and the red-baiting, blacklisting, jailing and deportation of people suspected of following communist or other left-wing ideology.
The testimony of Bentley and Chambers was cited as evidence of active Soviet and Communist infiltration of the United States government. Anti-communists also criticized the history of the Soviet Union and China as evidence of Communism's destructiveness, asserting that Stalin's purges, the creation of the gulag system and other examples of oppression were a function of the Communist ideology.
In 1947, Harry S Truman signed Executive Order 9835, creating the Federal Employees Loyalty Program. The program created review boards to investigate federal employees and terminate them if there were doubts as to their loyalty. The House Committee on Un-American Activities (HUAC) and the committees of Senator Joseph McCarthy began investigations of actual or alleged American Communists and their role in espionage, propaganda, and subversive activities, real and imagined.
There were also effects on America's way of life as a result of the Red Scare and the nuclear arms race, which contributed to the popularization of fallout shelters in home construction and regular duck and cover drills at schools. The Red Scare is also cited as one factor that contributed to the rise and popularity of science fiction films during the 1950s and beyond. Many thrillers and science fiction movies of the period used a theme of a sinister, inhuman enemy that was planning to infiltrate society and destroy the American way of life. Even a sports team was affected by the red scare; the Cincinnati Reds temporarily changed their team name to "Redlegs" to avoid the association of "Reds" and Communism.