Labor Day began because of death, murder of innocent workers by Federal troops.
The year was 1894, a time very much like now. The nation was undergoing an economic depression (the Panic of 1893). Unemployment was at 18% (currently the real unemployment is 16.7%). There was a Democratic president (Grover Cleveland) who was more interested in foreign affairs (Hawaiian annexation) than the economy in part because Republicans had block many of his reforms and in part because, as a pro-business Democrat, he was not concerned with the plight of the unemployed.
In 1894 the employees of the Pullman Palace Car Company went on strike. Pullman had fired nearly half his employees due to the depression. For the rest he had slashed wages while increasing their cost of living in his company town. Railway workers throughout the country joined the strike.
Rather than negotiate with his employees, Pullman and the other railroad men pressured President Cleveland into sending in federal troops as strikebreakers. The troops did what soldiers do. They attacked the workers until enough had died to end the strike.
President Cleveland compensated the workers for their lost jobs, lost wages, and lost lives with a holiday dedicated to them. The September date was chosen instead of May Day, which the rest of the world uses, because Cleveland was afraid of being called a communist.