Heilbronn League

The Heilbronn League was an alliance between Sweden, France, and the Protestant princes of Western Germany against the Catholic League during the Thirty Years' War. The treaty forming the League was signed at Heilbronn in Germany on April 23, 1633.

After the death of Gustavus Adolphus of Sweden, a greater number of German states were desperate to achieve peace. Nevertheless, Wallenstein's continuous military activity, as well as the diplomatic work carried out by Axel Oxenstierna, Sweden’s first minister, failed to bring about a permanent settlement. Most significantly, the search for a peace that would privilege all of those who signed it ensured the continuance of the war.

It was essential that France took on the role of the leader, and provide patronage to their German allies. Together they formed the Heilbronn League, which consisted of the Upper and Lower Rhenish, Swabian and Franconian military circles. Each of the circles was required to provide 2.5 million Reichstaler annually, while the Swedes retained their position as overall military commanders. France also agreed to increase the revenue that it would supply, as the death of Gustavus had caused France to have a greater influence on the military situation overall.

After the crushing Spanish-Imperial victory of Nördlingen, most of the German Protestant States were compelled to seek peace with the Emperor, who was now ready to come to terms and to relinquish the harshest provisions of the Edict of Restitution. Peace between the Emperor and the majority of German States was achieved by the Peace of Prague. This treaty was signed not only by Eastern Protestant States, like Saxony and Brandenburg (which were not parties of the Heillbronn League), but even by many Swedish allies in Western Germany. Thus, after the Peace of Prague, the Heillbronn League’s experience was virtually over. Legally speaking, this treaty affirmed that German States cannot enter in alliance treaties with other States. Swedish influence in the Rheinlander theatre vanished, and in the following years military operations were conducted under French leadership. A few former League’s members, especially Hesse, continued to fight against the Emperor until the final Peace of Westfalia.