I found myself thinking of the Haymarket Affair this May Day. It was one of our better reading groups at Melba. As I recall, the strike was held on the First of May to mark a national day of labor. After the horrible massacre, the Second International established May Day as an international day of labor in commemoration of those accused of the massacre, who were for the most part innocent of the crimes brought against them.
Seems the United States couldn't accept a holiday marked by Socialists around the world and eventually established its own labor day in September, whose origins apparently date back to the Knights of Labor, a tailor's organization, although the holiday was not recognized by Congress until 1894, five years after the Second International established May Day as Labor Day.
May Day is still celebrated throughout Europe, although it is largely associated with the former Soviet Union, but the US still holds onto such remnants of the celebration in the Maypole. Here are children doing a Maypole dance in Dover, Delaware,