Haymarket affair

An engraving of the Haymarket Square bombing

The Haymarket affair occurred on May 4, 1886 in Chicago, Illinois, United States. A strike began on May 1 seeking to reduce the work day to eight hours, and police soon killed striking workers. At a rally on May 4, an unidentified person threw a bomb at a group of police, killing some of them. Authorities then arrested the leadership of the anarchist labor movement and executed four people, two of whom were not even involved in the incident. Police later raided radical groups all over the country and arrested the entire leadership of the Knights of Labor.