Forty Years' War (Fidem Pacis)

The Forty Years' War was a series of wars fought mainly in central Europe that eventually dragged in most of the countries of Europe. It was one of the longest and most destructive conflicts in history before the modern era.

The war began with the election of Sigismund II, King of Bohemia, as Holy Roman Emperor. Unfortunately Sigismund was a Muslim, from a mainly Muslim country, and the staunchly Catholic rulers of the northern empire refused to accept his election. When the Pope in Mainz refused to crown Sigismund, the Catholic party took this as a pretext to overthrow him by force, and attacked Bohemia the next year in 1544.

Initially the war simply pitted the Muslim and Catholic states of the HRE against each other. However, as it dragged on with neither side able to gain an advantage over the other, neighbouring European states began to intervene, thus expanding the scope of the war.