May the first, Labour Day: why?? 五一万岁！！农工人万岁！！劳动节万岁！！

A Labour Day is an annual holiday celebrated all over the world that resulted from efforts of the labour union movement, to celebrate the economic and social achievements of workers.
The celebration of Labour Day has its origins in the eight hour day movement, which advocated eight hours for work, eight hours for recreation, and eight hours for rest. On 21 April 1856 Stonemasons and building workers on building sites around Melbourne, Australia, stopped work and marched from the University of Melbourne to Parliament House to achieve an eight hour day. Their direct action protest was a success, and they are noted as the first organized workers in the world to achieve an eight hour day with no loss of pay, which subsequently inspired the celebration of Labour Day and May Day.

The Haymarket Riot on May 4, 1886 in Chicago is generally considered to have been an important influence on the origin of international May Day observances for workers. In popular literature this event inspired the caricature of "a bomb-throwing anarchist." The causes of the incident are still controversial, although deeply polarized attitudes separating the business class and the working class in late 19th century Chicago are generally acknowledged as having precipitated the tragedy and its aftermath.

Source: Wikipedia