The Catholic League was a confederation of Catholic German states formed inorder to counteract the Protestant Union. Tension between these two groups would eventually ignite into the first phase of the Thirty Years War.

The founder of this league, and it's first commander, was Duke Maxamillian I of Bavaria. In 1609 the rulers of many small states within the Holy Roman Empire gathered at Munich to sign the treaty, which effectively bound them into a military alliance with a nine-year term. Near the end of the league's term, war broke out between Ferdinand II, Holy Roman Emperor, and Frederick V, Elector Palatine. The Protestant Union naturally sided with Frederick against the Catholic league, which supported Ferdinand. The league managed to defeat the Protestants in the first phase of the war.