"May 1, is International Workers' Day! It commemorates the sentencing to death of seven anarchist workers in Chicago who were wrongly convicted for throwing a bomb at police who attacked a strike demonstration in May 1886.
80,000 workers in Chicago had walked out on May 1 demanding a maximum 8-hour working day, alongside over 200,000 other workers across the US. Employers and the government were determined to crush the movement, and four of the anarchists were executed, with the fifth cheating the hangman by killing himself. An eighth was sentenced to 15 years' imprisonment. The surviving three were later pardoned, and the fight for the 8-hour day continued.
Before his execution, defendant August Spies told the court: "if you think that by hanging us you can stamp out the labour movement – the movement from which the downtrodden millions, the millions who toil and live in want and misery, the wage slaves, expect salvation – if this is your opinion, then hang us! Here you will tread upon a spark, but here, and there, and behind you, and in front of you, and everywhere, flames will blaze up. It is a subterranean fire. You cannot put it out."
Socialist and workers' organisations later chose May 1 to be celebrated as International Workers' Day, and today it is celebrated as a national holiday in many countries around the world, and an unofficial one in many others.
Learn more about the history of May Day in this book by Peter Linebaugh":

https://shop.workingclasshistory.com/products/the-incomplete-true-authentic-and-wonderful-history-of-may-day-peter-linebaugh

Pictured: the eight so-called Haymarket martyrs
(Taken from a Keith Preston post)