How was racial unrest linked to WWI?

The Red Scare was a somewhat paranoid fear that Communists
and Anarchists were at work to destroy the government of the United States. It is
related to World War I only in that it closely followed the Bolshevik Revolution in
Russia, and the fact that following the War, there was a tremendous eruption of
nativism. It was during this time that Sacco and Vanzetti were executed for robbery and
murder even though there was substantial doubt as to their guilt. Their Eastern European
origins and political affiliations were enough to convict them. The Boston Police Strike
was also an element, as it was commonly believed that labor unions were fronts for
Bolsheviks. The prime mover behind the Red Scare was Attorney General A. Mitchell Palmer
who used hyperbole, arrests and detentions based on flimsy evidence in his war against
the "Reds."

Racial unrest came about because of the Great
Migration. Many white Americans were fighting in the war, and a large number of blacks
moved North for jobs. They were not well received, and typically lived in segregated
neighborhoods. Their sudden presence in the North led to considerable racial
unrest.