五一国际劳动节源于美国芝加哥城的工人大罢工。

1886年5月1日，芝加哥的216816名工人为争取实行八小时工作制而举行大罢工，经过艰苦的流血斗争，终于获得了胜利。

为纪念这次伟大的工人运动，1889年7月，在恩格斯组织召开的第二国际成立大会上宣布将每年的五月一日定为国际劳动节。

May Day Fast Facts

CNN

Here's a look at May Day, referred to as International Workers' Day in many countries.

Facts:
Celebrated on the first day of May.

A holiday celebrating spring and/or working people. It is also often used as a day of civil protest.

History: 
The origins of May Day may go back to Pagan earth worship or to the spring festivals of ancient Egypt and India.

Another theory ties the holiday to the Roman festival of Floralia , a festival that honored Flora, the goddess of springtime. As Rome conquered other countries, the tradition spread.

Puritans in the United Stated looked down on May Day. As a result, the holiday is not celebrated as extensively in the United States.

In Medieval England, May Day celebrations centered on the maypole , which is a pole made from wood, decorated with streamers, which are held by dancers circling the pole.

In May of 1886, activists in the United States organized a national strike to promote an eight-hour workday. One of the protests, in Chicago's Haymarket Square, turned violent, with days of clashes between police and demonstrators. The incident came to be known as the Haymarket Affair.

To honor those who participated in the Haymarket protest, International Socialist Commission declared that May 1 would be a day designated for labor, called International Workers' Day. The holiday was established at a meeting in 1889.

In the United States, Labor Day is celebrated on the first Monday in September. It became a national holiday in 1894.