 Complete the following phrase:  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 