[2][3] The Protestant princes were supported by King Henry II of France, who was a Catholic, but sought to use the opportunity to expand his territory in modern-day Lorraine.

This previous conflict was settled by the Augsburg Interim, which left both camps unsatisfied, especially the princes who were forced to reconvert themselves and their population to Catholicism, although winning some concessions.

After laying the first contacts with Henry II, France declared war on the emperor in the autumn of 1551, and invaded Germany up to the Rhine.

Furthermore, in the Treaty of Chambord 15 January 1552, France promised financial and military aid to the princes, for which they were prepared to relinquish the Three Bishoprics of Metz, Verdun, and Toul, near the border, to the French king.

The troops of the allied princes quickly conquered the southern German cities that had remained loyal to the emperor, and advanced into Tyrol in March 1552.