 In 1630, Gustavus Adolphus of Sweden invaded Pomerania; partly to support his Protestant co-religionists, he also sought control of the Baltic trade, which provided much of Sweden's income.Economic issues meant Swedish intervention continued after Gustavus was killed in 1632, but led to conflict with Saxony, Brandenburg-Prussia and Denmark-Norway.Defeat at Nördlingen in September 1634 forced the Swedes to retreat, while most of their German allies made peace with Ferdinand in the 1635 Treaty of Prague.