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.