What was the era after WWI, when federal agenrs and police raided the homes of suspected radicals?

Answer 1

The first "Red Scare" in the U.S. occurred in the aftermath of WWI. In 1917, communist Bolshevists took over the Russian government and subsequently executed the Romanov royal family. Many Americans feared that this kind of revolutionary communism could come to the U.S., which at the time had a sizable population of recent immigrants from Eastern Europe (who might prove sympathetic to Russian radicalism). U.S. crackdown on radical agitators actually began during WWI. However, radical terrorists continued to plant bombs in cities across the nation, often targeting prominent public officials. One targeted man was President Wilson's Attorney General, Alexander Palmer. Empowered by espionage and sedition acts passed by Congress, from 1919-1920, Palmer instructed Justice Department agents to raid the homes of suspected militant radicals, collect evidence, and arrest plotters. Thousands of suspects were eventually arrested, and a few hundred were deported or chose to leave the U.S. for the Soviet Union. This program of mass arrests in such a short period of time came to be known as the "Palmer Raids" (named after the Attorney General who ordered them).

Answer 2

The Palmer Raids.
In November 1919, police arrested over 10,000 suspected radicals and communists, after allegations that they were planning to overthrow the US government.
See the link for details.

Answer 3

It was called the "Red Scare." IFrom 1919 to 1920 there was a series of strikes and terrorist attacks linked to left wing radical groups whose members were from Europe. These anarchists and Communists from Europe were rounded up and deported by the Federal government by the so-called "Palmer raids" under Attorney General A. Mitchell Palmer.

Answer 4

(sorry, I misread your question and focused on the wrong period, here is an answer that focused on the post-war period rather than the inter-war period. The general essence holds, but it is more of an epilogue to whatever right answer you may find)
Well, that is a bit general. In the US, as in Europe, there is a long history of ideological persecution dating back to the very roots of the Greco-Roman tradition. Ideological intolerance is a legal tradition defined by its continuity rather than its pauses, which were very few. That is to say that WWII is no watershed in the history of ideological persecution, and therefore it is not a helpful reference. Nonetheless, I take it you refer to the long red scare that followed WWII. This world-wide purge led to the imprisonment of the Rosenbergs under dubious legal procedures, the black listing of Hollywood "Reds" and government officials all under the guise of McCarthyism.
Now, you have to understand that the early post-war red scare is not the first red scare, and that the eroded labor movement lost all of its Great Depression momentum during the second European war (WWII) when union leaders became subservient to the state for the purpose of smoothing war-time production. After the Second War there were no headquarters to be raided, so the logical thing to do was to single out random highly visible individuals and accuse them of "communism". The raids, as far as i understand, only occurred against civil rights activists and thereafter against black nationalists. There was a whole FBI program set up to monitor and disable the Black Panthers, the SNCC and the SDS. In a demonstration of the repetition of historical patterns, government repression bred terrorism. In response to government aggression, the Black Panthers became ever-more belligerent and a splinter group of the SDS became the "Weather Underground". While Panthers and Weather People were both persecuted, the black nationalists received most of the blow. Black Panthers are assassinated and tortured until this very day.
What is most most relevant about the post-war red scare, is how it served to justify the world-wide crusade against nationalism. The Truman Doctrine gave origin to the international witch hunt against communism by intervening in the Greek Civil War on the side of the fascists and giving aid to France and Italy with the significant conditions that the aid would be withheld in the case of a Communist Party (CP) victory.
The Truman Doctrine's association of US global hegemony with ideological persecution became consolidated in the document NSC-68. A policy prescription devised by Paul Nitze which served as a blue print for the Cold War.
We could spend a few pages on it, but the point I am making is much too simple, that while a major propaganda campaign at home kept the US population wound up about communism and black nationalism, the US gov. was making plans to extend its control throughout the globe. So that, when the US pop. was freaking out about fallout shelters, the US gov. was toppling governments in Guatemala, Iran and Indonesia and imposing brutal anti-communist regimes. The real raids and slaughters of the post-war red scare occurred outside of the US, even if the persecutors were members of the US gov.

Answer 5

Are you asking about the McCarthy Era?
That was after WW II...
The American Communist Party, other left-wing organizations, and minority groups - including African-Americans, Native Americans, and various immigrant groups - became targets of suspicion, surveillance, and infiltration.
the House Un-American Activities Committee (HUAC) was charged with uncovering and identifying "anti-American" or "pro-communist" activities. A federal employee loyalty program was instituted in 1947 to preclude the employment of "disloyal Americans." Local governments, public institutions, and private companies, as well as universities and labor unions, quickly fell in line by instituting their own loyalty programs and dismissing employees suspected of having ties to communism.