On 1 May 1886, a quarter of a million workers went on strike in Chicago, closing businesses and flooding the streets with peaceful protesters demanding the eight-hour day. After a few days of protests, on 4 May, a bomb was thrown into a group of police officers killing seven, likely by an agent provocateur working for one of the industrialists. The police officers fired by shooting indiscriminately into the crowd, murdering dozens of peaceful protesters.
After the massacre, eight anarchists were charged and convicted of “conspiracy” in relation to the bomb, in spite of the lack of any proof any of them were involved. Seven were sentenced to death and one to life imprisonment; two of the death sentences were commuted and another of the men committed suicide rather than face the gallows. The remaining four were executed in 1887. One of the four was Albert Parsons, husband of Lucy Parsons. A few years later in 1893, the Illinois Governor pardoned the still-living convicts and criticised the unfair trial.
In the years following the massacre, the government embarked on a witchhunt of socialists and anarchists, arresting and even executing countless (as one example, arresting Eugene Debs following the Pullman Strike). Meanwhile, socialists and anarchists themselves chose to take to the streets in a peaceful march on 1 May every year, the anniversary commemorated as May Day.