A violent confrontation, since known as the Haymarket Affair, took place in Chicago, Illinois, May 4, 1886.
It was this occurrence that led to the establishment of International Workers' Day, commemorated every May 1.
The fact that other names include the Haymarket massacre, riot or incident all allude to the tragic events on that day.
A group of workers, supported by a rally, were striking in support of the eight-hour work day. Taking place at Haymarket Square in Chicago, the peaceful protest was marred when someone threw a dynamite bomb at police who were trying to disperse the crowds.
The bomb blast and following gunfire saw seven police officers killed along with four civilians. There were dozens of injuries.
The bomb's construction was the work of anarchists. Legal proceedings saw eight convicted of conspiracy with a range of punitive sentences handed out. Four were executed and one died by suicide.
This event is seen as the climax of the "Great Upheaval," social unrest among American working classes.
https://en.wikipedia.org/wiki/Haymarket_affair
