The history of the world holiday on the 1st May - May Day, or International Workers Day, held in commemoration of four anarchists executed for struggling for an 8-hour day.There is also a 3 part PBS video series that does quite a good presentation of the history of this event. Because PBS is under US government control (which, of course, is controlled by the One Percent), you need to make allowances for statements such as in Part 2 where carefully selected narrators and historians, while making reference to public reactions to the Haymarket riots, make statements like "Labor's largest paper called them [rioters] 'wild beasts'". Very likely this was in the newspaper of the AFL, a very conservative, pro-business labor union. Most other labor newspapers in the US, and indeed throughout the world, were very sympathetic to the protesting workers in Chicago. All were shocked by the barbarous response of the police and the extreme reaction by the legal establishment of the One Percent.
Then there were other statements made in the PBS program such as "It was very frightening to many people throughout the world" which implied that they were frightened by rioting anarchists. They were frightened mostly by the police repression. And, "Throughout the nation Americans were almost unanimous in the repression of the anarchists...they were seen to be a threat of the first order." This refers to mainstream media coverage and spokespeople for the One Percent. As you can see, some things have not changed much since 1886.
Generally, I think that too much emphasis was placed on the conflict at the McCormick Harvester plant which tended to suggest that the strikers were Luddites, that this was what caused the riots. This emphasis served to downplay the fight for an eight hour workday that workers had been struggling to obtain starting in 1863 when workdays for many were 12 hours. The conflict at the McCormick plant was a spark, but the fuel behind worker protests was the eight hour day objective.
Many working people felt that the bomb thrown at the police was by an agent provocateur to justify the extreme police crackdown.
PBS Part 1: Haymarket Martyrs--Origin of International Workers Day [5:13m]
PBS Part 2 [4:50m]
PBS Part 3 [5:17m]