What was the Red Scare that occurred in the US shortly after the end of World War 1?

Although the Red Scare is an American phenomenon, it is
rooted in the First World War and the 1917 Russian Revolution. While the U.S. was still
at war with Germany, the new Bolshevik government decided to sign a peace treaty with
Germany in 1918. The treaty meant that Germans had closed the eastern front of the war
and could concentrate more troops on its western front. Communist Russia was the new
target of American resentment and, by extension, American radicals and leftists were
regarded with suspicion and branded as "Red" (from the red flag of Communism). Wilson's
administration amassed thousands of troops to northern Russia and Siberia with the
official aim to safeguard these regions from Germany and Japan. In practice, however,
Wilson supported the anti-Bolsheviks forces in the civil war that had erupted after the
Revolution.

The Bolshevik victory and the 1919 call of the
Communist International for a world revolution made left-wing sympathizers an easy
target for American authorities. These militants were a perfect scapegoat for all the
post-war tensions that the nation was experiencing. The fear of an imminent Communist
revolution in the U.S. was sparked by a series of labor strikes that took place in 1919.
Wilson's administration used the rhetoric of fear of a revolution to put an end to the
strikes which had witnessed the involvement of many different professions from policemen
to steel workers. It is estimated that about 4 million workers were involved in the 1919
strikes. On May 1st, Labor Day, several bombs sent in the mail to notable Americans made
the threat of a revolution a palpable reality.

The American
Left was actually extremely divided into small factions and experienced a great deal of
in-fighting. It was thus very weak politically and unable to organize such a large scale
cospiration to lead to a Revolution. Yet, Wilson's administration created a Bureau of
Investigation, which, under J. Edgar Hoover's direction, arrested groups of radicals and
even deported foreigners such as Emma Goldman. The Bureau also suppressed civil
liberties in several cases, reaching a peak in the Palmer Raids of January 1920 when
government agents broke into the homes and offices of suspects with no search warrants
throughout the U.S. More than four thousand people were
arrested.