Although Maurice had been raised in the Lutheran faith, he converted to Calvinism in 1605. On the principle Cuius regio eius religio, Maurice's subjects were also required to convert to Calvinism. Maurice's conversion was controversial since the Peace of Augsburg had only settled religious matters betweens Roman Catholics and Lutherans and had not considered Calvinists. Maurice tried to introduce Calvinism to the lands which he had inherited from the extinct Hesse-Marburg branch of his family. Such a change of faith was contrary to the inheritance rules and resulted in an ongoing conflict with the Hesse-Darmstadt branch. It also brought him into conflict with the Holy Roman Emperor, Matthias.
Maurice's actions ruined Hesse-Kassel financially. In 1627 he abdicated in favour of his son William V. Maurice died in Eschwege.
