History of international workers' day!

May 1, 1886, Chicago socialists, reformists, anarchists, and ordinary workers combined to make the city the center of the national movement for an eight-hour day. Between April 25 and May 4, workers attended scores of meetings and paraded through the streets at least 19 times. On Saturday, May 1, 35,000 workers walked off their jobs. Tens of thousands more, both skilled and unskilled, joined them on May 3 and 4. Crowds traveled from workplace to workplace urging fellow workers to strike. Many now adopted the "radical demand of eight hours' work and increased wage". Police clashed with strikers at least a dozen times, three with shootings. 

At the McCormick reaper plant, a long-simmering strike erupted in violence on May 3, and police fired at strikers, killing at least two. On May 4 a peaceful meeting at Haymarket Square became even more so. The meeting was almost over and only about two hundred people remained when they were attacked by 176 policemen carrying Winchester repeater rifles. Then someone, unknown to this day, threw the first dynamite bomb ever used in peacetime history of the United States. The police panicked, and in the darkness many shot at their own men. Eventually, seven policemen died, . Four workers were also killed.

This incident came to be known as Haymarket massacre.The police rounded up suspicious foreign workers and anarchist leaders. Seven men stood trial for murder. On June 21, they were joined by an eighth — Parsons. He had fled the city after the bombing, but turned himself in to be tried with his comrades. No one had been identified as the bomber, but the eight defendants were tried as accessories to murder based on their inflammatory speeches. All of them were slapped with death penalty. No evidence was produced that they had made or thrown the bomb. The Chicago Tribune even offered to pay money to the jury if it found the eight men guilty.

On November 11, 1887, the prisoners were brought out to the hangman's platform. Albert Parsons, August Spies, George Engel, and Adolph Fischer stood before the crowd with hoods covering their faces. And then Spies spoke: "The day will come when our silence will be more powerful than the voices you are throttling today."

In 1889, the International Socialist Conference declared that, in commemoration of the Haymarket affair, May 1 would be an international holiday for labor, now known in many places as International Workers’ Day.

In June 1893, a Haymarket monument was unveiled in Chicago's Waldheim Cemetery. That same month Governor John Altgeld unconditionally pardoned Field, Neebe and Schwab because the trial and the conduct of the judge had been shamefully unjust. 

In the U.S., that holiday came in for particular contempt during the anti-communist fervor of the early Cold War. In July of 1958, President Eisenhower signed a resolution named May 1 “Loyalty Day” in an attempt to avoid any hint of solidarity with the “workers of the world” on May Day. The resolution shamelessly declared that it would be “a special day for the reaffirmation of loyalty to the United States of America and for the recognition of the heritage of "American freedom".”