International Workers' Day traces back to the founding congress of the Second International in Paris in 1889, which chose May 1 to commemorate the 1886 Haymarket affair in Chicago, when workers striking for an eight-hour workday clashed violently with police. The date quickly spread as an international symbol of labour solidarity, and by 1890 workers across multiple countries were marching in coordinated demonstrations. Today it is a public holiday in more than 160 countries, making it one of the most widely observed days in the world, even though it was never formally proclaimed by the United Nations — its authority comes instead from more than a century of continuous labour and trade-union tradition. Unions and governments use the occasion to take stock of working conditions, campaign for fair wages, and push for safer workplaces. Observances vary widely: large public marches and rallies in some countries, quieter family holidays in others, and official ceremonies honoring workers' contributions elsewhere. Whatever the form, the day keeps alive the memory that many of today's basic labour protections — the eight-hour day chief among them — were won through sustained collective struggle.