After the end of the Bohemian War , the League's army fought in central Germany, but was defeated at the Battle of Mingolsheim on 27 April 1622, after which they joined with the Spanish to fight and win the Battle of Wimpfen against the Margrave of Baden-Durlach on May 6. Following these victories, the army captured the city of Heidelberg , the capital of the leader of the Protestant Union, following an eleven-week siege on September 19. The Protestant prince Christian, Duke of Brunswick-Lüneburg , raised another army, but was defeated at the Battle of Stadtlohn where 13,000 out of his army of 15,000 were lost. This victory virtually ended all Protestant resistance in Germany. This caused Denmark's king Christian IV to enter the Thirty Years' War in 1625 to protect Protestantism and also in a bid to make himself the primary leader of Northern Europe.