Given the task definition and input, reply with output. 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.

Though it is not France, this polity was co-ruled by a man who assumed the name Charles VIII and was put down when trying to take full control of one of its constituents. This polity captured Flensburg after fighting for control over the Oresund with its chief rival. Its power was challenged with lower class uprisings led by Engelbrecht Engelbrechtson and had to be reinstated in an event led by Jorgen Holmuth whose targets were supporters of Sten Sture the Younger. That event, the Stockholm Bloodbath, occurred during Christian II's authority over this confederation. Its creation was solidified by the Coronation Letter establishing a hereditary monarchy begun by Eric of Pomerania. Engineered by Queen Margaret I in 1397, for 10 points, name this Scandinavian confederation of Norway, Sweden, and Denmark
History