Treaty of Stettin (1570)

Frederick underlined his claim by using the Union's three crowns in his coat of arms and invading Sweden in 1563; both actions are considered the starting events of the Seven Years' War.

[5] In July 1570, Maximilian II, Holy Roman Emperor, initiated a peace congress in Stettin (after 1945 Szczecin), aiming to mediate between Sweden and Denmark.

[4] Several diplomats acted as mediators: The host, Pomeranian duke Johann Friedrich of Pomerania-Stettin, acted as head of the delegates sent by his emperor, Maximilian; French envoy at the Danish court Charles Dancey, who had been heavily involved in the preparation of the congress, was among the mediators; Martin Kromer, bishop of Warmia (Ermland) and others were sent by the Polish king Sigismund Augustus; Augustus of Saxony attended in person.

Of the parties, Denmark was represented by Peder Bille (Bilde), Jørgen Rosenkrantz, Henrik Rantzau, Niels Kaas, and Joachim Henke (Hinck); Sweden sent baron Jöran Gera, Bengt Gylta, Erik Gyllenstjerna (Gyllenstierna), and others.

John III was determined to keep his only port on the Scandinavian west coast, and his efforts included the sale of warships and devaluation of the Swedish currency.