Some people celebrate May Day today with a pagan celebration of flowers and Maypoles; others recognize it as a day of protest and worker solidarity. That history goes back to 1886 when 200,000 U.S. workers struck for an eight-hour day. On the third day, a Chicago strike at the McCormick Reaper plant became violent as police killed and injured the strikers. The next day’s peaceful meeting at Haymarket Square protesting police action turned even more brutal. As the meeting started to break up, a bomb near the speaker’s wagon wounded 60 policemen and killed another seven. The police wounded 200 civilians and killed several more. Although no one was sure who had committed the crime, four people were executed. No one in the U.S. had an eight-hour day until the United Mine Workers in 1898; a federal law mandating the eight-hour day wasn’t passed until 1938.

The international holiday for labor, created in…