The Duke of Geldern's War (1543-1546) was a conflict primarily between the Duchy of Geldern and the Holy Roman Empire. The war arose from territorial disputes, as the Duke of Geldern sought to expand his influence in the region. The conflict involved various local powers and alliances, leading to a series of battles and sieges. The war concluded with the Treaty of Venlo in 1546, which reaffirmed the Duchy of Geldern as part of the Holy Roman Empire. This treaty marked the end of the duke's ambitions and solidified imperial control over the region, impacting the political landscape of northern Europe.