In 1886 Chicago, the push for an eight-hour workday brought more than 300,000 workers nationwide off the job on May 1. Two days later, police fired into strikers at the McCormick Harvesting Machine Company plant, killing at least two. Anarchists led by August Spies, editor of the Arbeiter-Zeitung, called a rally at Haymarket Square for May 4; Spies had a call to arms struck from the flyers, and 20,000 new ones were printed. Mayor Carter Harrison judged the rainy rally peaceful and went home, but Inspector John Bonfield then marched 176 officers toward the speakers’ wagon, and a dynamite bomb thrown from an alley killed Officer Mathias J. Degan.

The firefight that followed, with heavy friendly fire, left seven police officers and an estimated four to eight civilians dead. With no idea who threw the bomb, State’s Attorney Julius Grinnell tried eight anarchists on the theory that their speeches and writings had inspired the unknown bomber, before Judge Joseph Gary and a hand-picked jury. All eight were convicted, seven sentenced to death. Louis Lingg killed himself with a smuggled blasting cap, and Spies, Albert Parsons, George Engel and Adolf Fischer were hanged on November 11, 1887. In 1893 Governor John Peter Altgeld pardoned the three survivors and lost his career for it.

• Only two of the eight defendants, Samuel Fielden and Spies, were at the rally when the bomb exploded.
• Oscar Neebe got 15 years, apparently for trying to revive the shuttered Arbeiter-Zeitung.
• Historian Timothy Messer-Kruse, after studying the trial transcripts, argues the proceedings were less anomalous for 1886 than long believed.
• The 1889 police statue in Haymarket Square was hit by a streetcar in 1927 and blown up twice by the Weather Underground, then moved inside the Chicago Police Academy.
• In 1889 the Second International adopted May 1 to honor the Haymarket martyrs, creating International Workers’ Day.