Siege of Stralsund (1628)  The Siege of Stralsund was a siege laid on Stralsund by Albrecht von Wallenstein's Imperial Army during the Thirty Years' War, from May to 4 August 1628. Stralsund was aided by Denmark and Sweden, with considerable Scottish participation. The lifting of the siege ended Wallenstein's series of victories, and contributed to his downfall. The Swedish garrison in Stralsund was the first on German soil in history. The battle marked the "de facto" entrance of Sweden into the war. Christian IV of Denmark had declared war on the Holy Roman Empire in 1625. He had then invaded the empire with an army commanded by Ernst von Mansfeld to oppose the Catholic League's army commanded by Johann Tserclaes, Count of Tilly. In response, Ferdinand II, Holy Roman Emperor, had Albrecht von Wallenstein raise an additional army to support Tilly. Wallenstein defeated Mansfeld in the Battle of Dessau Bridge in 1626. The remnants of Mansfeld's army left Central Germany, and turned to Silesia and Hungary to regroup with Gabriel Bethlen's forces. After Tilly had defeated Christian IV in the Battle of Lutter am Barenberge in August 1626, and Bethlen was neutralized in the (third) Peace of Pressburg in December, Tilly and Wallenstein were able to subsequently expel Christian IV from the North German plain, organized in the Lower Saxon and Upper Saxon imperial circles, and pressure him even in Danish Jutland. The internally divided Upper Saxon circle, to which the Duchy of Pomerania with Stralsund belonged, was incapable of self-defence and had formally declared neutrality. Christian IV's army staff heavily relied on Scottish expertise: with 300 Scottish officers in his service, Scottish officers outnumbered Danish and Norwegian officers combined by 3:1. Also, Christian IV had issued patents to raise 9,000 Scottish troops in 1627, adding to 2,000-3,000 Scottish troops raised by Donald Mackay for Ernst von Mansfeld's army, but who had been deployed to Denmark instead. Gustavus Adolphus of Sweden was since 1626 involved in the Polish-Swedish War, with Poland allied to the Holy Roman Empire. In this war, Scotsman Alexander Leslie started his career in Swedish service as commandant and governor of Pillau in East Prussia. Gustavus Adolphus had made plans to intervene in the Holy Roman Empire, of which the Riksdag commission approved in the winter of 1627/28.