1653 Imperial election electoral rights in a treaty of 1619, confirmed at the Diet of Regensburg on February 25, 1623. The revolt ignited a broader religious war across Germany, the Thirty Years' War, which would involve not only the states of the empire but also Sweden, the Dutch Republic, France, Denmark–Norway, England, Scotland, Spain and Hungary and which would kill some eight million people before its end. The Peace of Westphalia which ended the war in 1648 revived the principle of "cuius regio, eius religio" established in 1555 by the Peace of Augsburg and established the modern concept of Westphalian sovereignty. It additionally
Hessian War Peace Congress mediated by Duke Ernest of Saxe-Gotha and which resulted in a unification and peace treaty that was sealed in April 1648, ahead of the Treaty of Westphalia itself. Before the Westphalian Peace Treaty, Cassel fought one last time against the imperial side, winning the Battle of Wevelinghoven in the Rhineland, together with other Protestant troops. Darmstadt, however, was not involved in this battle. Under the Unification Treaty between Cassel and Darmstadt, Upper Hesse was permanently divided. Darmstadt had to give up a significant part of Upper Hesse to Cassel, not least Marburg and other occupied territories, including the