Religious reform in Switzerland was begun by Huldrych Zwingli, a Catholic priest in Zurich. In 1520, Zwingli openly attacked abuses in the Catholic Church. He called for a return to the more personal faith of early Christianity. He also wanted believers to have more control over the Church. In 1531, a bitter war between Swiss Protestants and Catholics broke out. During the fighting, Zwingli met his death. Meanwhile, John Calvin, then a young law student in France with a growing interest in Church doctrine, was beginning to clarify his religious beliefs. When Martin Luther posted his 95 Theses in 1517, John Calvin had been only eight years old. Calvin grew up to have an much influence in the spread of Protestantism as Luther did. He would give order to the faith Luther had begun. In 1536, Calvin published Institutes of the Christian Religion. This book expressed ideas about God, salvation, and human nature.