The Musso war was an armed conflict between the federation of the Three Leagues (Drei Bünde) in the Grisons, an associate state of the Old Swiss Confederacy, and the Duchy of Milan early in the 16th century. The refusal of the Catholic cantons to support the Three Leagues in these skirmishes was taken by the Swiss canton of Zürich as the reason to start the second war of Kappel. The Catholic cantons would emerge victorious from that war and even gain the majority in the confederacy's federal assembly, the Tagsatzung, with far-reaching consequences for the confederacy.