Torstensson with rigor suppressed the intrigues against Sweden which were secretly carried on within the army. Brandenburg received a new elector in Frederic William, who, ambitious and far-seeing, entered an alliance with the victorious power of the North. Torstensson now was enabled to invade the imperial crown lands, commencing with Silesia; but finding it necessary to force a battle he met the imperialists at Breitenfeld. October 23, 1642, the second great victory of Breitenfeld was won by Swedish arms. Archduke Leopold and Piccolomini led the imperial army, the latter general fighting as a common soldier to inspire courage by his example, but with no effect. The Swedes captured the baggage, cannon and banners of the enemy, taking 5,000 prisoners and leaving as many dead imperialists on the field. Torstensson conquered Leipsic on the following day.
Torstensson marched through Bohemia and Moravia with the rapidity which characterized all his military movements, and penetrated to the very gates of Vienna, the emperor with difficulty saving himself from being made his prisoner. But suddenly he left and marched through Silesia to North Germany. He had received an order from the state council to attack Denmark. The great chancellor was out of patience with the perfidy and intrigues of Christian IV., who stood in secret connection with every one of Sweden’s enemies. No previous declaration of war was made. Torstensson captured the Danish duchies of Schleswig and Holstein before any one could prevent it, his army then taking possession of all Jutland. Gustavus Horn invaded Scania, almost completely capturing the whole province in spite of bands of freebooters among the peasants, called _Snaphaner_.
Denmark was in danger of its very existence, but King Christian IV. did not forget his old wish to destroy the town of Gothenburg, whose growing prosperity caused him envy. He approached Gothenburg with a fleet, and viewed the town from the overlooking mountain of the Ramberg. His demands for a surrender were refused. Patriotic Louis de Geer had ordered from Holland a fleet at his own expense, which was to go to the support of Gothenburg. It did not arrive in time, but King Christian left to meet it, and it later proved of great value in the Swedish movements at sea, joining the Swedish fleet in the Sound. The latter, consisting of twenty-two ships under the command of Clas Fleming, sailed to the Danish waters, capturing the island of Femern, supported by Torstensson. An invasion of the island of Funen was planned, but could not be effected. A great naval battle between the Swedish and Danish fleets was fought July 6th. It caused great loss on either side, without being decisive. King Christian, who commanded his naval forces, lost one eye and received over twenty different wounds. The Swedes kept the place of battle, but sought the Bay of Skiel for repairs, where they were hedged in by the Danish fleet. Clas Fleming encouraged his followers to cut through the line, in which they were successful. A month later he was killed by a shot from the coast of Holstein, where the Danes had erected a fort. The Swedes avenged the death of their valiant commander by destroying the fort and killing its defenders. Fleming was succeeded by Charles Gustavus Wrangel, who saved the fleet to Sweden, returning to Femern in the autumn, joined by the Dutch fleet of Louis de Geer. The Danish fleet was met with October 13th, and at once scattered. The swift-sailing Dutch ships went in pursuit and destroyed all the seventeen Danish ships but two, which brought the news of the disaster to Copenhagen.