<P> The Peace of Augsburg contained three main principles: </P> <Ol> <Li> The principle of cuius regio, eius religio ("Whose realm, his religion") provided for internal religious unity within a state: the religion of the prince became the religion of the state and all its inhabitants . Those inhabitants who could not conform to the prince's religion were allowed to leave: an innovative idea in the 16th century . This principle was discussed at length by the various delegates, who finally reached agreement on the specifics of its wording after examining the problem and the proposed solution from every possible angle . </Li> <Li> The second principle, called the reservatum ecclesiasticum (ecclesiastical reservation), covered the special status of the ecclesiastical state . If the prelate of an ecclesiastic state changed his religion, the inhabitants of that state did not have to do so . Instead, the prelate was expected to resign from his post, although this was not spelled out in the agreement . </Li> <Li> The third principle, known as Declaratio Ferdinandei (Ferdinand's Declaration), exempted knights and some of the cities from the requirement of religious uniformity, if the reformed religion had been practiced there since the mid-1520s . This allowed for a few mixed cities and towns where Catholics and Lutherans had lived together . It also protected the authority of the princely families, the knights and some of the cities to determine what religious uniformity meant in their territories . Ferdinand inserted this at the last minute, on his own authority . </Li> </Ol> <Li> The principle of cuius regio, eius religio ("Whose realm, his religion") provided for internal religious unity within a state: the religion of the prince became the religion of the state and all its inhabitants . Those inhabitants who could not conform to the prince's religion were allowed to leave: an innovative idea in the 16th century . This principle was discussed at length by the various delegates, who finally reached agreement on the specifics of its wording after examining the problem and the proposed solution from every possible angle . </Li> <Li> The second principle, called the reservatum ecclesiasticum (ecclesiastical reservation), covered the special status of the ecclesiastical state . If the prelate of an ecclesiastic state changed his religion, the inhabitants of that state did not have to do so . Instead, the prelate was expected to resign from his post, although this was not spelled out in the agreement . </Li>

What was the cause of the peace of augsburg is signed in 1555