Violence broke out as a consequence of Martin Luther's protests against the Catholic Church, a protest that began with the Ninety-Five Theses on the Power and Efficacy of Indulgences he posted on the door of All Saints' Church in Wittenbeg, Germany. Among the many violent insurrections was the bloody Peasants War in Germany, between 1524 and 1525, in which the peasant class, led by the Protestant clergy, revolted against the aristocracy for economic and religious persecutions. By 1547, the Holy Roman Emperor Charles V knew that peace between religious factions needed to be established and issued the Augsburg Interim of 1548. However, the peace established under the Augsburg Interim was only temporary, mostly because it primarily reflected Catholic views. By 1555, Charles V understood that a new peace treaty would need to be issued and proclaimed the Peace of Augsburg.
The Peace of Augsburg forbade any rulers from waging future wars based on religious grounds. It also legally recognized the two separate churches, the Roman Catholics and the Lutherans.
Some of the treaty's most important principles concerned governing, in an effort to establish peace by unifying people under one religion or the other in any one area. More specifically, the treaty made it legal to have only one church in any region of the empire, and the church was decided upon by the ruler of the region, not the subjects. But any subjects who objected to the religion of the ruler were free to move from the territory. Furthermore, the treaty granted rulers' legal freedom to change religions if wanted while also legally protecting citizens from likewise having to change religions.
The one exception to rulers choosing the religion of an area applied to the Free Imperial Cities that had evolved into self-ruling cities beginning in the 13th and 14th centuries. Such cities included the French cities of Comar, Haguenau, Mulhouse, and Strasbourg; the German cities of Augsburg, Cologne, Memmingen, Ravensburg; and the Switzerland city of Basel. Since these cities were already self-governing, they had already achieved religious integration (Encyclopaedia Britannica, "Peace of Augsburg").