The Peace of Augsburg, also called the Augsburg Settlement, was a treaty between Charles V, Holy Roman Emperor, and the Schmalkaldic League, signed in September 1555 at the imperial city of Augsburg. It officially ended the religious struggle between the two groups and made the legal division of Christianity permanent within the Holy Roman Empire, allowing rulers to choose either Lutheranism or Roman Catholicism as the official confession of their state. However, the Peace of Augsburg arrangement is also credited with ending much Christian unity around Europe. Calvinism was not allowed until the Peace of Westphalia. The Peace of Augsburg has been described as "the first step on the road toward a European system of sovereign states." The system, created on the basis of the Augsburg Peace, collapsed at the beginning of the 17th century, which was one of the reasons for the Thirty Years' War. Overview The Peace ran over the principle Cuius regio, eius religio ("whose realm, his religion"), which allowed the princes of states within the Holy Roman Empire to adopt either Lutheranism or Catholicism within the domains they controlled, ultimately reaffirming their sovereignty over those domains. Subjects, citizens, or residents who did not wish to conform to the prince's choice were given a grace period in which they were free to emigrate to different regions in which their desired religion had been accepted. Article 24 stated: "In case our subjects, whether belonging to the old religion or the Augsburg Confession, should intend leaving their homes with their wives and children to settle in another, they shall be hindered neither in the sale of their estates after due payment of the local taxes nor injured in their honor." Charles V had made an interim ruling, the Augsburg Interim of 1548, on the legitimacy of two religious creeds in the empire, and this was codified in law on 30 June 1548 upon the insistence of Charles V, who wanted to work out religious differences under the auspices of a general council of the Catholic Church. The Interim largely reflected principles of religious behavior in its 26 articles, although it allowed for marriage of the clergy, and the giving of both bread and wine to the laity. This led to resistance by the Protestant territories, who proclaimed their own Interim at Leipzig the following year. The Interim was overthrown in 1552 by the revolt of the Protestant elector Maurice