The Diet of Speyer was convened in March 1529, for action against the Turks, whose armies were pressing forward in Hungary, and would besiege Vienna later in the year, and against the further progress of Protestantism.
The Catholic dignitaries appeared in full force, as did various princes and representatives of imperial cities who were leaning towards Luther and Zwingli's reforms.
Ascendant Roman Catholic forces, particularly given Charles V's recent successes against the French in Italy, aimed to reverse the policy of religious tolerance adopted in 1526.
[2] The Lutheran members of the Diet, under the well-founded impression that the prohibition of any future reformation meant death to the whole movement, entered, in the legal form of an appeal on behalf of themselves, their subjects and all Christians, a protest on 25 April 1529.
[3] The document was signed by the Elector John of Saxony, Margrave George of Brandenburg, Dukes Ernest and Francis of Braunschweig-Luneburg, Landgrave Philip of Hesse, Prince Wolfgang of Anhalt, and the representatives of fourteen imperial cities, including Strassburg and St. Gall of the Zwinglian persuasion.