May 1st, International Workers' Day, commemorates the historic struggle of working people throughout the world, and is recognized in most countries. The struggle for the eight-hour day began in the 1860s. In 1884, the Federation of Organized Trades and Labour Unions of the United States and Canada, organized in 1881 (and changing its name in 1886 to American Federation of Labour) passed a resolution which asserted that "eight hours shall constitute a legal day's work from and after May 1, 1886, and that we recommend to labour organizations throughout this district that they so direct their laws as to conform to this resolution".

The following year the Federation repeated the declaration that an eight-hour system was to go into effect on May 1, 1886. With workers being forced to work ten, twelve, and fourteen hours a day, support for the eight-hour movement grew rapidly. In the months prior to May 1, 1886, thousands of workers, organized and unorganized, members of the organization Knights of Labour and of the federation, were drawn into the struggle. Chicago was the main centre of the agitation for a shorter day. The anarchists were in the forefront of the Central Labour Union of Chicago, which consisted of 22 unions in 1886, among them the seven largest in the city.

During the Railroad strikes of 1877, the workers had been violently attacked by the police and the United States Army. A similar tactic of state terrorism was prepared by the bureaucracy to fight the eight-hour movement. The police and National Guard were increased in size and received new and powerful weapons financed by local business leaders. Chicago's Commercial Club purchased a $2000 machine gun for the Illinois National Guard to be used against strikers. Nevertheless, by May 1st, the movement had already won gains for many Chicago workers. But on May 3, 1886, police fired into a crowd of strikers at the McCormick Harvester Machine Company, killing at least one striker, seriously wounding five or six others, and injuring an undetermined number.

The meeting proceeded without incident, and by the time the last speaker was on the platform, the rainy gathering was already breaking up, with only about two hundred people remaining. It was then a police column of 180 men marched into the square and ordered the meeting to disperse. At the end of the meeting a bomb was thrown at the police, killing one instantly, six others died later. About seventy police officers were wounded. Police responded by firing into the crowd. How many civilians were wounded or killed from police bullets never was ascertained exactly. Although it was never determined who threw the bomb, the incident was used as an excuse to attack anarchists and the labour movement in general. Police ransacked the homes and offices of suspected radicals, and hundreds were arrested without charge. A reign of police terror swept over Chicago. Staging "raids" in the working-class districts, the police rounded up all known anarchists and other socialists. "Make the raids first and look up the law afterward!" publicly counselled the state's attorney.