The conclusion of treaties by the Republic of Poland and the Elector of Brandenburg in Welawa and Bydgoszcz in 1657 was a turning point in the Polish-Swedish war, begun in 1655. The elector of Brandenburg, Frederick Wilhelm, joined the anti-Swedish coalition in exchange for exemption from subordination to Prussia. Conducting a prudent and balanced policy, he aimed to increase his political position through both military participation and diplomatic efforts. The goal of Frederick Wilhelm’s policy was to achieve the greatest possible benefits in the ongoing war, including acquiring territorial gains. Faced with efforts to conclude a general peace that would end the war, at the same time opening the way towards creating a new political order in the central and northern part of Europe, Elector Frederick Wilhelm, who gained the position of a party to the conflict, made his own proposals for peace negotiations planned in Oliwa. Among Brandenburg’s postulates was, amongst other things, the issue of extending the provisions of treaties concluded in 1657 with Poland in Welawa and Bydgoszcz, which would also create international guarantees for them.