during the 1620s, and with the town of Stralsund under siege by imperial troops, its ruler Bogislaw XIV, Duke of Stettin, concluded a treaty with King Gustavus Adolphus of Sweden in June 1628. On 10 July 1630, the treaty was extended into an 'eternal' pact in the Treaty of Stettin (1630). By the end of that year, the Swedes