The city's councillors had been emboldened by King Gustavus Adolphus's landing in Pomerania on 6 July 1630. The Swedish king was a Lutheran Christian, and many of Magdeburg's residents were convinced that he would aid them in their struggle against the Roman Catholic Habsburg emperor, Ferdinand II. However, not all Protestant princes of the Holy Roman Empire had immediately embraced Adolphus; some believed his chief motive for entering the war was to take northern German ports, which would allow him to control commerce in the Baltic Sea.