How did the Treaty of Oliva affect Poland’s authority over Ducal Prussia?

The Treaty of Oliva, signed in 1660, formally confirmed the end of Poland’s suzerainty over Ducal Prussia.12

Prior to this, the electors of Brandenburg had held the duchy as a Polish fief. However, during the First Northern War, the "Great Elector" Frederick William maneuvered diplomatically to secure his independence from the Polish crown. This process began with the Treaty of Wehlau in 1657, in which King John II Casimir Vasa renounced Polish suzerainty in exchange for military support against Sweden.213

The Treaty of Oliva ratified these earlier agreements, effectively stripping Poland of its authority over the territory and recognizing Frederick William and his heirs as the sovereign rulers of Ducal Prussia. This shift was a significant turning point, as it allowed the Hohenzollerns to establish full sovereignty over the duchy, distinct from their other territories that remained under the theoretical suzerainty of the Holy Roman Empire.124