Haymarket Affair, Chicago, 1886

On 1 May 1886 hundreds of thousands of American workers struck for the eight-hour day. Two days later police killed several strikers at the McCormick works in Chicago, and a protest meeting was called for the Haymarket. It was peaceful and thinning out in the rain when police advanced to disperse it; someone threw a dynamite bomb, killing a policeman. Officers opened fire in the dark. Seven policemen and an unknown number of civilians died, most of the police apparently by their colleagues' bullets.

Eight anarchists were tried. The prosecution conceded it could not identify the bomber and argued that their speeches and writings had incited whoever did it. Seven were sentenced to death. One took his own life in the cell, four were hanged in November 1887, and two had their sentences commuted. In 1893 Governor John Peter Altgeld pardoned the survivors, writing that the trial had been conducted with a prejudiced jury and no evidence connecting the defendants to the crime; the pardon ended his political career. The Second International chose 1 May as international workers' day in memory of the case, which is why most of the world marks it — and the United States does not.