Treaty of Bromberg - Historical Context

Historical Context

The Duchy of Prussia was established as a Polish fief under duke Albrecht (Albert) in the Treaty of Cracow of 8 April 1525. The fief was hereditary, and in case Albrecht or his brothers' house went extinct in the male line, Cracow provided for it to pass on to the Polish king, who would then be obliged to appoint a German-speaking Prussian-born governor. On 4 June 1563, this provision was changed by Polish king Sigismund II Augustus in a privilege issued at Petrikau, which in addition to Albrechts branch of the House of Hohenzollern (Hohenzollern-Ansbach) also allowed the Brandenburg branch of the Hohenzollern as possible successors. This privilege provided for the succession of the Brandenburgian electors as Prussian dukes upon the extinction of the House of Hohenzollern-Ansbach in 1618.

In 1656, during the early Second Northern War, the Brandenburgian Hohenzollern first took the Prussian duchy and Ermland (Ermeland, Warmia) as Swedish fiefs in the Treaty of Königsberg, before the Swedish king released them from the vassalage and made them absolute sovereigns in these provinces. After fighting alongside with the Swedish army in 1656, most prominently in the Battle of Warsaw, Hohenzollern Frederick William I was willing to abandon his ally when the war had turned against them, and signalled his willingness to change sides if Polish king John II Casimir Vasa would grant him similar privileges as previously the Swedish king Charles X Gustav - these conditions were negotiated in Wehlau (Welawa, now Znamensk) and Bromberg (Bygost, Bydgoszcz).

The Polish interest in an alliance with Brandenburg-Prussia was born out of the need to end the war with Sweden as soon as possible. On 3 November 1656, the Truce of Vilna had promised Alexis of Russia's election as successor on the Polish throne at the next diet in turn for halting his offensive in Poland-Lithuania and fight Sweden instead. While in the Grand Duchy of Lithuania there was support for this treaty among the nobles, who hoped for more privileged positions, this was not true for the Kingdom of Poland, where the elites looked for ways to circumvent Alexis' succession. To quickly end the war with Sweden and thus be able to avoid the implementation of Vilna, the anti-Swedish alliance had to be extended. The new-won Russian ally was reluctant to support Poland against Sweden as long as no diet had confirmed Vilna. A second ally, the Austrian Habsburgs were won in the first and second Vienna treaties, yet as the Habsburg forces were to be maintained by Poland, this alliance's prize was bound to rise the longer the war lasted. A third ally was Denmark-Norway, who joined the anti-Swedish coalition in June 1657 triggered by the second treaty of Vienna. Yet, Denmark was not fighting on Polish soil, and although her involvement bound Charles X Gustav's forces and a formal alliance with Poland-Lithuania was concluded in July, the Danish war aim was to recover Scandinavian territories lost in the Second Treaty of Brömsebro (1645).

The Habsburgs' interest in the treaty was to build up good relations to Frederick William I, who as a prince-elector was a valuable ally if he was won to support their policy in the Holy Roman Empire. Thus, the Habsburgs were interested in Frederick William I changing from the Swedish to their camp, and sent diplomat Franz Paul Freiherr von Lisola to mediate a respective settlement.

Bromberg and Wehlau are regarded as "twin treaties", "suplementary treaties" or one treaty, sometimes referred to as "Treaty of Wehlau and Bromberg" or "Treaty of Wehlau-Bromberg."