Haymarket affair

The Haymarket affair, also known as the Haymarket massacre, the Haymarket riot, the Haymarket Square riot, or the Haymarket Incident, was the aftermath of a bombing that took place at a labor demonstration on May 4, 1886, at Haymarket Square in Chicago, Illinois, United States. The rally began peacefully in support of workers striking for an eight-hour work day, the day after the events at the McCormick Harvesting Machine Company, during which one person was killed and many workers injured. An unknown person threw a dynamite bomb at the police as they acted to disperse the meeting, and the bomb blast and ensuing retaliatory gunfire by the police caused the deaths of seven police officers and at least four civilians; dozens of others were wounded.

Eight anarchists were charged with the bombing. In the internationally publicized legal proceedings against the accused, the eight were convicted of conspiracy.

Source: Wikipedia