Discontent was growing in the Holy Roman Empire over the decisions made at the 1548 Augsburg Diet, the so-called "Geharnischter Reichstag" ("armour-clad Diet"). In the north, the Protestant princes secretly formed an alliance by the Treaty of Torgau of 22 May 1551. They included "inter alia" John Albert of Mecklenburg, Albert of Prussia, William of Hesse-Kassel, and Albert Alcibiades of Brandenburg-Kulmbach. They sought to defend Protestantism and the "Teutonic Liberty" ("teutsche Libertät"), which meant the freedom of the Imperial Princes. They also planned to liberate Philip of Hesse, who was incarcerated by the emperor in 1547. 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.