You will be given a definition of a task first, then some input of the task.
In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.

Benjamin Butler represented some of the men convicted after this event, all of whom were later pardoned by John Peter Altgeld. Immediately preceded by a fight at the McCormick Harvesting Machine Co. at which four were killed by police, this event is commemorated by bonfires at some May Day celebrations. For ten points, name this tragedy that helped lead to the downfall of the Knights of Labor; a May 4th, 1886 riot touched off when someone detonated a bomb at a labor rally in Chicago.
Output:
History