The Day has its origin in the USA.  In the late nineteenth century, the working class was in constant struggle to gain the 8-hour work day. Conditions were severe, and it was quite common for labourers to work 10 to 16 hours a day in unsafe conditions.

Death and injury were commonplace, and no compensation was given to the victims' families. There was no insurance for workers' safety, and they were hardly given any days off. To put it simply, they were treated more as machines, and not living beings.

At its national convention in Chicago, held in 1884, the Federation of Organized Trades and Labor Unions (which later became the American Federation of Labor), proclaimed that "eight hours shall constitute a legal day's labor from and after 1 May, 1886." 

An estimated quarter million workers in the Chicago area became directly involved in the crusade to implement the eight-hour work day. There grew a sense of a greater social revolution beyond the more immediate gains of shortened hours, but a drastic change in the economic structure of capitalism.

Not surprisingly, the entire city was prepared for mass bloodshed. On 1 May, 1886, more than 300,000 workers in 13,000 businesses across the United States walked off their jobs on the first May Day celebration in history.

In Chicago, the epicentre for the 8-hour day agitators, 40,000 went out on strike, with the anarchists in the forefront of the public's eye. More and more workers continued to walk off their jobs until the numbers swelled to nearly 100,000, yet peace prevailed.

It was not until two days later, 3 May, 1886, that violence broke out between police and strikers.

For the next six months, violence continued between the police and the workers.

Full of rage, a public meeting was called by some of the anarchists for the following day in Haymarket Square to discuss the police brutality. Due to bad weather and short notice, only about 3,000 of the tens of thousands of people showed up from the day before.

This affair included families with children and the mayor of Chicago himself. Upon hearing of this gathering, the police arrived and started to disperse the crowd. During this time, a bomb was thrown near the police vehicles and personnel (it could not be identified who threw the bomb).

Enraged, the police fired into the crowd, killing as many as eight civilians and wounding forty more. Many of the prominent protesters were arrested, convicted and put on trial, and most were given capital punishment.

In 1889, the International Socialist Conference declared that in commemoration of the Haymarket affair, and to pay respect to the innocent victims, 1 May would be an international holiday for labour, now known in many places as International Workers' Day.

Ever since then, May Day is observed as a holiday all around the globe.

For most countries, Labour Day is synonymous with, or linked with, International Workers' Day. For other countries, Labour Day is celebrated on a different date, often one with special significance for the labour movement in that country.