After the treaty, Frederick William I first continued his military support for Charles X Gustav by detaching some forces to join the latter's Polish campaigns in early 1657.
However, after Denmark entered the war and Charles X Gustav left the Polish theater to campaign in Denmark, Frederick William I withdrew his forces from Poland and entrenched them in his Prussian territories.

When an envoy of Ferdinand III, Holy Roman Emperor proposed Polish acceptance of Hohenzollern sovereignty in Prussia in turn for Frederick William I joining the anti-Swedish camp and supporting the Habsburg candidate in the next imperial elections, the "Great Elector" signaled his willingness to change sides.
Thereupon, Polish king John III Sobieski concluded the secret Treaty of Wehlau on 19 September 1657, wherein the Hohenzollern sovereignty over the Duchy of Prussia, but not Ermland, was confirmed in turn for an "eternal alliance" between Brandenburg-Prussia and Poland and religious freedom for the Catholics in Prussia.

The terms of Wehlau was confirmed by the Treaty of Bromberg in November, after which Brandenburg actively campaigned against Sweden.
Frederick William I also gave his vote to the Habsburg candidate, after the emperor on 29 February 1658 agreed to another treaty providing Frederick William I with 10,000 forces to support his campaign in Swedish Pomerania.

On 18 January 1701, based on the sovereignty of the Prussian duchy, Frederick I of Prussia crowned himself "King in Prussia."
After the treaty, Frederick William I first continued his military support for Charles X Gustav by detaching some forces to join the latter's Polish campaigns in early 1657. However, after Denmark entered the war and Charles X Gustav left the Polish theater to campaign in Denmark, Frederick William I withdrew his forces from Poland and entrenched them in his Prussian territories.
When an envoy of Ferdinand III, Holy Roman Emperor proposed Polish acceptance of Hohenzollern sovereignty in Prussia in turn for Frederick William I joining the anti-Swedish camp and supporting the Habsburg candidate in the next imperial elections, the "Great Elector" signaled his willingness to change sides. Thereupon, Polish king John III Sobieski concluded the secret Treaty of Wehlau on 19 September 1657, wherein the Hohenzollern sovereignty over the Duchy of Prussia, but not Ermland, was confirmed in turn for an "eternal alliance" between Brandenburg-Prussia and Poland and religious freedom for the Catholics in Prussia.
The terms of Wehlau was confirmed by the Treaty of Bromberg in November, after which Brandenburg actively campaigned against Sweden. Frederick William I also gave his vote to the Habsburg candidate, after the emperor on 29 February 1658 agreed to another treaty providing Frederick William I with 10,000 forces to support his campaign in Swedish Pomerania.
On 18 January 1701, based on the sovereignty of the Prussian duchy, Frederick I of Prussia crowned himself "King in Prussia."
Treaty of Labiau