1538-1543
When Charles of Guelders died without an heir on June 30, 1538, he had done everything he could to find an other successor than Emperor Charles V. He had appointed William, Duke of Jülich-Cleves-Berg, related through his great-grandfather Reinald IV, Duke of Guelders and Jülich (1365-1423), as his successor. William allied himself with the King of France and married Jeanne d'Albret. When the Low Countries were at war with France, he sent in 1542 Maarten van Rossum on a raid through Brabant, plundering the countyside and besieging Antwerp and Leuven. These attacks were countered by Mary of Hungary (governor of the Netherlands) and Louis of Praet.
As a reaction, Mary of Hungary sent an army toward Guelders and Jülich, which were conquered in 1543, after two failed earlier attempts. In the Treaty of Venlo, William of Jülich was forced to cede the Duchy of Guelders and the County of Zutphen to Charles V, but was allowed to keep Jülich.
This treaty concluded the formation of the Seventeen Provinces and the determination of the border between the Netherlands and Germany.
Read more about this topic: Guelderian Wars