Johann Tserclaes, Count of Tilly was a field marshal who commanded the Catholic League's forces in the Thirty Years' War. From 1620–31, he had an unmatched and demoralizing string of important victories against the Protestants, including White Mountain, Wimpfen, Höchst, Stadtlohn and the Conquest of the Palatinate. He destroyed a Danish army at Lutter and sacked the Protestant city of Magdeburg, which caused the death of some 20,000 of the city's inhabitants, both defenders and non-combatants, out of a total population of 25,000.

The Catholic League was a coalition of Catholic states of the Holy Roman Empire formed 10 July 1609. While initially formed as a confederation to act politically to negotiate issues vis-à-vis the Protestant Union, modelled on the more intransigent ultra-Catholic French Catholic League (1576), it was subsequently concluded as a military alliance "for the defence of the Catholic religion and peace within the Empire".