By 1886 the state of Illinois had enacted an 8-hour Workday law. Employers in Illinois, however, refused to obey the law, and government refused to enforce it. Labor Unions called for a general strike, and parade to be held on May 1, 1886. This parade, and the events which followed, are the basis for Mayday celebrations in many industrial Nations, but not in The US.
The work stoppage, strikes and meetings which followed the May 1 kickoff were met with increasingly violent resistance by business and government. On the evening of may 4th, someone threw a bomb at police who had come to suppress a public rally in Haymarket Square. One policeman was killed in the blast, and an unknown number of people were killed or wounded in the massacre which ensued when police responded.
Police quickly rounded up Union organizers, many of which were professed Anarchists. In a famously partisan trial, most were found guilty of conspiring to bomb police, were sentenced and most executed.  The execution of the 5 condemned men who refused to admit their guilt and accept a commuted sentence, was reported to have been exceedingly gruesome, the hangman's nooses failed to break the necks of any of the five, and they slowly strangled to death.