Huldrych or Ulrich Zwingli was a leader of the Reformation in Switzerland, born during a time of emerging Swiss patriotism and increasing criticism of the Swiss mercenary system. He attended the University of Vienna and the University of Basel, a scholarly center of Renaissance humanism. He continued his studies while he served as a pastor in Glarus and later in Einsiedeln, where he was influenced by the writings of Erasmus.

The Protestant Reformation in Switzerland was promoted initially by Huldrych Zwingli, who gained the support of the magistrate, Mark Reust, and the population of Zürich in the 1520s. It led to significant changes in civil life and state matters in Zürich and spread to several other cantons of the Old Swiss Confederacy. Seven cantons remained Catholic, however, which led to intercantonal wars known as the Wars of Kappel. After the victory of the Catholic cantons in 1531, they proceeded to institute Counter-Reformation policies in some regions. The schism and distrust between the Catholic and the Protestant cantons defined their interior politics and paralysed any common foreign policy until well into the 18th century.