Thus Sweden held, for a time, the control of the principal trade routes of the Baltic up to the very confines of the empire; and the increment of revenue resulting from this commanding position was of material assistance during the earlier stages of the war in Germany, whither Gustavus transferred his forces in June 1630. Gustavus, later to be called "the Lion of the North" due to his skills as a commander, intervened on the Protestant side in the German civil war. Using new military techniques such as lighter and more mobile artillery and cavalry shocks, he won an astounding victory at the Battle of Breitenfeld in 1631. In the Battle of Lützen on November 6, 1632, he was killed, though, and Sweden lost their warrior-king. The battle itself was a draw, but two years later the tide turned at Nördlingen, where Imperial troops won a convincing victory over the Protestant Army. In order to prevent the Habsburgs from winning the war, France, who had already given subsidies to Sweden following the Treaty of Bärwalde (1631), intervened on the Protestant side. The war dragged on for many years until a peace agreement was at last reached in 1648.