In 1529, after enlisting the help of the leaders of the forest cantons,[3] Zwingli attempted to reform the cantons by force. However, the winning diplomacy of the Union forced the Protestants to not cross the border, postponing the conflict until 1531.
The canton of Zürich was the principal supporter of Zwingli and the movement of Swiss reformation. When they fought the Musso War against the Duchy of Milan, the member states of the Catholic Union refused to provide aid. Zwingli immediately sanctioned the Catholic cantons.
^The forest cantons - or "Waldkantone" - refer to the four heavily forested and mountainous cantons at the shore of Lake Lucerne, namely Uri, Schwyz, Unterwalden and Lucerne. Lucerne, though quite flat otherwise, has a heavily forested bight at Lake Lucerne; and Unterwalden has later split into Obwalden and Nidwalden.