The War of the Jülich Succession, also known as the Jülich War or the Jülich-Cleves Succession Crises (German: Jülich-Klevischer Erbfolgestreit), was a war of succession in the United Duchies of Jülich-Cleves-Berg. The first phase of the war lasted between 10 June 1609 and 24 October 1610, with the second phase starting in May 1614 and finally ending on 13 October 1614. At first, the war pitted Catholic Archduke Leopold V against the combined forces of the Protestant claimants, Johann Sigismund, Elector of Brandenburg and Wolfgang Wilhelm of Palatinate-Neuburg, ending in the former's military defeat. The representatives of Brandenburg and Neuburg later entered conflict amongst themselves, partly due to religious conversions, which led to the resumption of hostilities.
The war was further complicated by the involvement of Spain, the Dutch Republic, France, England, and the Protestant Union, making it closely tied to the Eighty Years' War, as well as part of the European wars of religion. It also corresponded to a Protestant uprising in the Free Imperial City of Aachen. It was finally settled by the Treaty of Xanten, whose provisions favored Spain, though the conflict was not fully resolved until later.
By the early 17th century, the rapid spread of the Lutheran and Calvinist doctrines after the Protestant Reformation was met by a period of Roman Catholic resurgence, known as the Counter-Reformation. Such interdenominational conflicts such as the Cologne War and the Strasbourg Bishops' War prompted the creation of the Catholic League and the Protestant Union, with the intention of safeguarding the interests of the Holy Roman Empire's Catholic and Protestant nobility, respectively. Growing tensions led to war in 1609, when a succession crisis in the United Duchies of Jülich-Cleves-Berg sparked the War of the Jülich Succession. The territories in question covered an area of 14,000 km² and had both geopolitical importance from their proximity to the Spanish Road and a booming economy, which was fueled by refugees fleeing the lands that were being ravaged by the Eighty Years' War. The immediate cause of war was the death of John William, Duke of Jülich-Cleves-Berg on 25 March 1609, who was affected by serious mental illness, and left no heirs to succeed him.
Part of the succession dispute came from laws that had been established by William the Rich, Duke of Jülich-Cleves-Berg and father of John William. William had established two major laws, the Privilegium Unionis and Priviligium Successionis, the privileges of Union and Succession respectively. The Privilegium Unionis had declared that the Duchies of Jülich, Cleves, and Berg, which had recently been united in 1521, would continue to be inherited as one, rather than be divided. The Priviligium Successionis declared that in the case of the extinction of the male line (which is what happened when John William died), the duchies would pass to a female line. However, the nature of this female succession was not clear, in that it was not obvious whether or not the duchies should pass through the eldest female, the eldest living female, or the eldest male descendent of a female.
Emperor Rudolf II had claims to the duchies stemming from intermarriage. However, he was unable to declare his intentions openly without compromising his perceived neutrality. A total of six other claimants appeared, with rulers of the Margraviate of Brandenburg and Palatinate-Neuburg having the only credible claims through their relationship to John William's sisters. However, the nature of the claims were different. Johann Sigismund of Brandenburg claimed the duchies through his wife, a granddaughter of William the Rich, and the most senior female descendent of William the Rich. However, Wolfgang Wilhelm of Neuburg, son of Phillip Ludwig, Count Palatine of Neuburg, held a claim through his mother, a direct daughter of William, hence he was the most senior male descendent. Rudolf II's indecision in selecting a person to succeed John William would create a power vacuum that allowed parties to sought to exploit, creating numerous factions in the duchies.
Neuburg was a relatively young principality, established during the War of the Landshut Succession. It was small and weak, surrounded by stronger powers like Bavaria and the Electoral Palatinate. Thus, acquiring the Jülich succession was a major goal of Neuburg. Not only would it provide more land for Neuburg, but the territories in question were rich and could help the economy of Neuburg as well. As Neuburg had benefited from aligning with the Emperor in the past, despite their Lutheran religious status, Wolfgang Wilhelm had personally travelled to Prague to gain Imperial support. Neuburg also attempted to contact France and England. However, all of this failed.
The Electorate of Brandenburg, also officially Lutheran, was also interested in the Jülich territories, but unlike Neuburg would not be able to count on Imperial support. Brandenburg had challenged the Emperor recently during the Strasbourg War, so tensions between the two parties were still high. Thus, Brandenburg sought allies, particularly amongst major protestant powers both foreign and in the Empire. Though they had failed to acquire support from Denmark-Norway, negotiations with the Dutch Republic had been successful. Emboldened by these alliances, Brandenburg was unwilling to accept a compromise deal from Neuburg, instead claiming the entirety of the duchies for themselves.
Despite the matter being a contest over a relatively small amount of land, the succession quickly grew to be an international issue. The Dutch Republic, fiercely anti-Habsburg, did a not want a pro-Habsburg figure to inherit the duchies. Hence, the Dutch had been eager to form an alliance with the likeminded Electorate of Brandenburg, who was also anti-Habsburg. France also had interests in the region. Henry IV of France, like the Dutch, was opposed to a pro-Habsburg ruler in Jülich-Cleves-Berg (see French–Habsburg rivalry). Despite being a Catholic, Henry IV wanted to ensure that a Protestant would inherit the duchies, but he didn't necessarily care who. As such, he contacted Landgrave Maurice of Hesse-Kassel, explaining that a united Protestant cause was required to keep the Habsburgs away. A large number of Protestant princes would also support this sentiment. Frederick IV, Elector Palatine and head of the Protestant Union, wished for a peaceful settlement. Johann of Nassau-Siegen shared the same thoughts and told Maurice as such. Henry IV of France also tried to garner support from other Protestant princes, namely Wurttemberg.
Maurice agreed, but despite his efforts, it was impossible to have Brandenburg and Neuburg agree on a settlement, as both parties believed their claim was best. When the ailing John William finally died on 25 March 1609, both Neuburg and Brandenburg rushed to claim the duchies. However, the privy council that had governed Jülich-Cleves-Berg through John William's madness refused to accept either of them, and continued to rule on their own by establishing a regency council, which included the late duke's wife, Antonia of Lorraine, and an imperial commissioner sent by Emperor Rudolf II. On 24 May, Rudolf II, who had the authority to dictate a final settlement over the succession, announced that the Aulic Council (one of the two Supreme Courts in the Holy Roman Empire) was to provide a definite verdict within four weeks.
Brandenburg and Neuburg, who viewed the regency as a direct attempt at undermining their claims, finally agreed to a provisional settlement, with mediation from Maurice of Hesse-Kassel. When Joachim Ernst, a representative of Johann Sigismund, passed by Kassel on his way to Jülich, Maurice convinced him to negotiate with Wolfgang Wilhelm. On 10 June 1609, they met in Dortmund and signed the Treaty of Dortmund (1609), rejecting all other claimants, and establishing a provisional government together with the local estates.