Why did Johan van Oldenbarnevelt act like the foreign secretary of the United Provinces?

Johan van Oldenbarnevelt functioned as the de facto foreign secretary of the United Provinces primarily because he served as the landsadvocaat (chief minister) of Holland, the wealthiest and most influential province in the union.12

Although he was technically a servant of only one province, Holland contributed nearly 59 percent of the federal budget, making it the dominant political force in the country. By filling the power vacuum left after the reconquest of Brabant and Flanders by Spanish forces, Oldenbarnevelt became the primary advocate for the union's interests.13

In this capacity, he mobilized the nation's resources and conducted critical diplomatic missions to France and England, successfully integrating the new commonwealth and securing international recognition. His role allowed him to coordinate the republic's foreign policy, most notably through the 1596 triple alliance and the Twelve Years’ Truce of 1609.14