Labor Day is a day of rest that commemorates years of war. Congress inaugurated the holiday just days after President Grover Cleveland sent 12,000 federal troops to break the Pullman strike. The tactics were bloody; US deputy marshals killed two men and wounded many more.
That was 1894, an election year. Cleveland needed a way to win workers back to his side. He saw an opportunity in a federal holiday honoring workers — as well as organized labor.
And this from Tim Goulet:
In reality, however, Labor Day started twelve years earlier — even before the 1886 Haymarket events that inspired May Day — with a mass rally in New York. On September 5, 1882, socialists, the Knights of Labor, and various left organizations associated with the Central Labor Union (CLU) organized a march calling for shorter hours, higher pay, safer working conditions — and a labor holiday. That year, New York had been the scene of spirited labor struggles. On January 30, thousands of workers thronged Cooper Union to support Irish tenants protesting their British landlords.