Answer: The event you are referring to is known as the Haymarket Affair or the Haymarket Riot. It occurred in Chicago, Illinois, in 1886. The incident took place during a labor protest rally demanding an eight-hour workday at Haymarket Square. As the rally was nearing its end, a bomb was detonated, killing seven policemen and injuring many others. In the aftermath, the police opened fire on the crowd, resulting in the death of four laborers.
The Haymarket Affair gained significant attention and led to a highly controversial trial. Although there was no direct evidence linking the defendants to the bombing, four anarchists were convicted and later executed. This event had a profound impact on the labor movement in the United States. The Knights of Labor, a prominent labor organization at the time, experienced a decline in membership, and unionism became associated with radicalism in the eyes of many Americans. The Haymarket Affair remains a significant event in the history of labor rights and the struggle for workers' rights in the United States.