<P> In the Cologne War, Spanish troops expelled the former prince - archbishop and replaced him with Ernst of Bavaria, a Roman Catholic . After this success, the Catholics regained peace, and the principle of cuius regio, eius religio began to be exerted more strictly in Bavaria, Würzburg, and other states . This forced Lutheran residents to choose between conversion or exile . Lutherans also witnessed the defection of the lords of the Palatinate (1560), Nassau (1578), Hesse - Kassel (1603), and Brandenburg (1613) to the new Calvinist faith . Thus, at the beginning of the 17th century, the Rhine lands and those south to the Danube were largely Catholic, while Lutherans predominated in the north, and Calvinists dominated in certain other areas, such as west - central Germany, Switzerland, and the Netherlands . Minorities of each creed existed almost everywhere, however . In some lordships and cities, the numbers of Calvinists, Catholics, and Lutherans were approximately equal . </P> <P> Much to the consternation of their Spanish ruling cousins, the Habsburg emperors who followed Charles V (especially Ferdinand I and Maximilian II, but also Rudolf II, and his successor Matthias) were content to allow the princes of the empire to choose their own religious policies . These rulers avoided religious wars within the empire by allowing the different Christian faiths to spread without coercion . This angered those who sought religious uniformity . Meanwhile, Sweden and Denmark - Norway, both Lutheran kingdoms, sought to assist the Protestant cause in the Empire, and wanted to gain political and economic influence there, as well . </P> <P> Religious tensions broke into violence in the German free city of Donauwörth in 1606 . There, the Lutheran majority barred the Catholic residents of the Swabian town from holding an annual Markus procession, which provoked a riot . This prompted foreign intervention by Duke Maximilian of Bavaria on behalf of the Catholics . After the violence ceased, Calvinists in Germany (who remained a minority) felt the most threatened . They banded together and formed the League of Evangelical Union in 1608, under the leadership of the Elector Palatine Frederick IV, whose son, Frederick V, married Elizabeth Stuart, the Scottish - born daughter of King James VI of Scotland and I of England and Ireland . The establishment of the league prompted the Catholics into banding together to form the Catholic League in 1609, under the leadership of Duke Maximilian . </P> <P> Tensions escalated further in 1609, with the War of the Jülich Succession, which began when John William, Duke of Jülich - Cleves - Berg, the ruler of the strategically important United Duchies of Jülich - Cleves - Berg, died childless . Two rival claimants vied for the duchy . The first was Duchess Anna of Prussia, daughter of Duke John William's eldest sister, Marie Eleonore of Cleves . Anna was married to John Sigismund, Elector of Brandenburg . The second was Wolfgang William, Count Palatine of Neuburg, who was the son of Duke John William's second - eldest sister, Anna of Cleves . Duchess Anna of Prussia claimed Jülich - Cleves - Berg as the heir to the senior line, while Wolfgang William, Count Palatine of Neuburg, claimed Jülich - Cleves - Berg as Duke John William's eldest male heir . Both claimants were Protestants . In 1610, to prevent war between the rival claimants, the forces of Rudolf II, Holy Roman Emperor occupied Jülich - Cleves - Berg until the Aulic Council (Reichshofrat) resolved the dispute . However, several Protestant princes feared that the emperor, a devout Catholic, intended to keep Jülich - Cleves - Berg for himself to prevent the United Duchies falling into Protestant hands . Representatives of Henry IV of France and the Dutch Republic gathered forces to invade Jülich - Cleves - Berg, but these plans were cut short by the assassination of Henry IV by the Catholic fanatic François Ravaillac . Hoping to gain an advantage in the dispute, Wolfgang William converted to Catholicism; John Sigismund, though, converted to Calvinism (although Anna of Prussia stayed Lutheran). The dispute was settled in 1614 with the Treaty of Xanten, by which the United Duchies were dismantled: Jülich and Berg were awarded to Wolfgang William, while John Sigismund gained Cleves, Mark, and Ravensberg . </P>

Which was a cause of world war 2 in europe yahoo