On May 1, 1886, workers in Chicago organized a peaceful rally in support of an eight-hour workday, which escalated into violence after a bomb exploded near the police. The bombing killed seven officers and at least four civilians, and it led to a crackdown on labor movements in the United States. The incident became known as the Haymarket Affair and had lasting effects on labor rights in the U.S. Several anarchists were wrongfully convicted of the bombing, though there was no conclusive evidence of their involvement. The event is commemorated annually as International Workers Day in many parts of the world.