Today is an official public holiday in Croatia, the 1st of May, and International Worker’s Day or Labour Day or May Day. The day, which is a celebration of workers and the working class, dates back to 1886 in Chicago. The Haymarket Affair was a peaceful rally in support of workers who were striking to try and get an eight-hour week. However, the rally turned fatal when someone threw a bomb at the police officers, killing seven and injuring dozens. It was seen as retaliation for the police killing eight workers trying to disperse the crowd.
The 1904 Sixth Conference of the Second International, called on "all Social Democratic Party organisations and trade unions of all countries to demonstrate energetically on the First of May for the legal establishment of the 8-hour day, for the class demands of the proletariat, and for universal peace."
The first of May is a national, public holiday in many countries across the world, in most cases as "Labour Day", "International Workers' Day" or some similar name – although some countries celebrate a Labour Day on other dates significant to them.