The Battle of Sempach was fought on 9 July 1386, between Leopold III, Duke of Austria and the Old Swiss Confederacy. The battle was a decisive Swiss victory in which Duke Leopold and numerous Austrian nobles died. The victory helped turn the loosely allied Swiss Confederation into a more unified nation and is seen as a turning point in the growth of Switzerland .

During 1383 and 1384, the expansion of the Old Swiss Confederacy collided with Austrian interests. The interests of Austria were further undermined in the Pact of Constance, a union of Zürich, Zug , Solothurn and 51 cities of Swabia. In 1385, there were various attacks, without formal declaration of war or central organization, by forces of Zürich, Zug and Lucerne on the Austrian strongholds of Rapperswil , Rothenburg, Cham and Wolhusen .