Before the Thirty Years' War hostilities reached the Lower Saxon Circle, the chiefs of state of its members were alarmed and prepared for the worst. So in 1625 they elected from their midst the Lutheran Duke Christian IV of Holstein, simultaneously King of Denmark, the new Lower Saxon Circle Colonel, i.e. the commander in chief of the joint circular forces. In this function Christian IV allied with Ernst von Mansfeld in a military campaign and planned to start in Thuringia in Middle Germany, and then take to its south. His intention was to bring relief to German Protestants, who had been severely defeated a few weeks earlier in the Battle of Dessau Bridge.
With the participation of Christian IV, the Thirty Years' War, which had hitherto been confined to opposing factions of the Holy Roman Empire, now extended to other European powers, though Christian, as Duke of Holstein, was not a complete foreigner.