Banner undertook this bold enterprise. His military reputation had suffered by his last retreat from Bohemia, and it stood in need of some great exploit to restore its former lustre. Without communicating his designs to any one, in the depth of the winter of 1641, as soon as the roads and rivers were frozen, he broke up from his quarters in Lunenburg. Accompanied by Marshal Guebriant, who commanded the armies of France and Weimar, he took the route towards the Danube, through Thuringia and Vogtland, and appeared before Ratisbon, ere the Diet could be apprised of his approach. The consternation of the assembly was indescribable; and, in the first alarm, the deputies prepared for flight. The Emperor alone declared that he would not leave the town, and encouraged the rest by his example. Unfortunately for the Swedes, a thaw came on, which broke up the ice upon the Danube, so that it was no longer passable on foot, while no boats could cross it, on account of the quantities of ice which were swept down by the current. In order to perform something, and to humble the pride of the Emperor, Banner discourteously fired 500 cannon shots into the town, which, however, did little mischief. Baffled in his designs, he resolved to penetrate farther into Bavaria, and the defenceless province of Moravia, where a rich booty and comfortable quarters awaited his troops. Guebriant, however, began to fear that the purpose of the Swedes was to draw the army of Bernard away from the Rhine, and to cut off its communication with France, till it should be either entirely won over, or incapacitated from acting independently. He therefore separated from Banner to return to the Maine; and the latter was exposed to the whole force of the Imperialists, which had been secretly drawn together between Ratisbon and Ingoldstadt, and was on its march against him. It was now time to think of a rapid retreat, which, having to be effected in the face of an army superior in cavalry, and betwixt woods and rivers, through a country entirely hostile, appeared almost impracticable. He hastily retired towards the Forest, intending to penetrate through Bohemia into Saxony; but he was obliged to sacrifice three regiments at Neuburg. These with a truly Spartan courage, defended themselves for four days behind an old wall, and gained time for Banner to escape. He retreated by Egra to Annaberg; Piccolomini took a shorter route in pursuit, by Schlakenwald; and Banner succeeded, only by a single half hour, in clearing the Pass of Prisnitz, and saving his whole army from the Imperialists. At Zwickau he was again joined by Guebriant; and both generals directed their march towards Halberstadt, after in vain attempting to defend the Saal, and to prevent the passage of the Imperialists.

Banner, at length, terminated his career at Halberstadt, in May 1641, a victim to vexation and disappointment. He sustained with great renown, though with varying success, the reputation of the Swedish arms in Germany, and by a train of victories showed himself worthy of his great master in the art of war. He was fertile in expedients, which he planned with secrecy, and executed with boldness; cautious in the midst of dangers, greater in adversity than in prosperity, and never more formidable than when upon the brink of destruction. But the virtues of the hero were united with all the railings and vices which a military life creates, or at least fosters. As imperious in private life as he was at the head of his army, rude as his profession, and proud as a conqueror; he oppressed the German princes no less by his haughtiness, than their country by his contributions. He consoled himself for the toils of war in voluptuousness and the pleasures of the table, in which he indulged to excess, and was thus brought to an early grave. But though as much addicted to pleasure as Alexander or Mahomet the Second, he hurried from the arms of luxury into the hardest fatigues, and placed himself in all his vigour at the head of his army, at the very moment his soldiers were murmuring at his luxurious excesses. Nearly 80,000 men fell in the numerous battles which he fought, and about 600 hostile standards and colours, which he sent to Stockholm, were the trophies of his victories. The want of this great general was soon severely felt by the Swedes, who feared, with justice, that the loss would not readily be replaced. The spirit of rebellion and insubordination, which had been overawed by the imperious demeanour of this dreaded commander, awoke upon his death. The officers, with an alarming unanimity, demanded payment of their arrears; and none of the four generals who shared the command, possessed influence enough to satisfy these demands, or to silence the malcontents. All discipline was at an end, increasing want, and the imperial citations were daily diminishing the number of the army; the troops of France and Weimar showed little zeal; those of Lunenburg forsook the Swedish colours; the Princes also of the House of Brunswick, after the death of Duke George, had formed a separate treaty with the Emperor; and at last even those of Hesse quitted them, to seek better quarters in Westphalia. The enemy profited by these calamitous divisions; and although defeated with loss in two pitched battles, succeeded in making considerable progress in Lower Saxony.

At length appeared the new Swedish generalissimo, with fresh troops and money. This was Bernard Torstensohn, a pupil of Gustavus Adolphus, and his most successful imitator, who had been his page during the Polish war. Though a martyr to the gout, and confined to a litter, he surpassed all his opponents in activity; and his enterprises had wings, while his body was held by the most frightful of fetters. Under him, the scene of war was changed, and new maxims adopted, which necessity dictated, and the issue justified. All the countries in which the contest had hitherto raged were exhausted; while the House of Austria, safe in its more distant territories, felt not the miseries of the war under which the rest of Germany groaned. Torstensohn first furnished them with this bitter experience, glutted his Swedes on the fertile produce of Austria, and carried the torch of war to the very footsteps of the imperial throne.

In Silesia, the enemy had gained considerable advantages over the Swedish general Stalhantsch, and driven him as far as Neumark. Torstensohn, who had joined the main body of the Swedes in Lunenburg, summoned him to unite with his force, and in the year 1642 hastily marched into Silesia through Brandenburg, which, under its great Elector, had begun to maintain an armed neutrality. Glogau was carried, sword in hand, without a breach, or formal approaches; the Duke Francis Albert of Lauenburg defeated and killed at Schweidnitz; and Schweidnitz itself with almost all the towns on that side of the Oder, taken. He now penetrated with irresistible violence into the interior of Moravia, where no enemy of Austria had hitherto appeared, took Olmutz, and threw Vienna itself into consternation.

But, in the mean time, Piccolomini and the Archduke Leopold had collected a superior force, which speedily drove the Swedish conquerors from Moravia, and after a fruitless attempt upon Brieg, from Silesia. Reinforced by Wrangel, the Swedes again attempted to make head against the enemy, and relieved Grossglogau; but could neither bring the Imperialists to an engagement, nor carry into effect their own views upon Bohemia. Overrunning Lusatia, they took Zittau, in presence of the enemy, and after a short stay in that country, directed their march towards the Elbe, which they passed at Torgau. Torstensohn now threatened Leipzig with a siege, and hoped to raise a large supply of provisions and contributions from that prosperous town, which for ten years had been unvisited with the scourge of war.

The Imperialists, under Leopold and Piccolomini, immediately hastened by Dresden to its relief, and Torstensohn, to avoid being inclosed between this army and the town, boldly advanced to meet them in order of battle. By a strange coincidence, the two armies met upon the very spot which, eleven years before, Gustavus Adolphus had rendered remarkable by a decisive victory; and the heroism of their predecessors, now kindled in the Swedes a noble emulation on this consecrated ground. The Swedish generals, Stahlhantsch and Wellenberg, led their divisions with such impetuosity upon the left wing of the Imperialists, before it was completely formed, that the whole cavalry that covered it were dispersed and rendered unserviceable. But the left of the Swedes was threatened with a similar fate, when the victorious right advanced to its assistance, took the enemy in flank and rear, and divided the Austrian line. The infantry on both sides stood firm as a wall, and when their ammunition was exhausted, maintained the combat with the butt-ends of their muskets, till at last the Imperialists, completely surrounded, after a contest of three hours, were compelled to abandon the field. The generals on both sides had more than once to rally their flying troops; and the Archduke Leopold, with his regiment, was the first in the attack and last in flight. But this bloody victory cost the Swedes more than 3000 men, and two of their best generals, Schlangen and Lilienhoeck. More than 5000 of the Imperialists were left upon the field, and nearly as many taken prisoners. Their whole artillery, consisting of 46 field-pieces, the silver plate and portfolio of the archduke, with the whole baggage of the army, fell into the hands of the victors. Torstensohn, too greatly disabled by his victory to pursue the enemy, moved upon Leipzig. The defeated army retired into Bohemia, where its shattered regiments reassembled. The Archduke Leopold could not recover from the vexation caused by this defeat; and the regiment of cavalry which, by its premature flight, had occasioned the disaster, experienced the effects of his indignation. At Raconitz in Bohemia, in presence of the whole army, he publicly declared it infamous, deprived it of its horses, arms, and ensigns, ordered its standards to be torn, condemned to death several of the officers, and decimated the privates.

The surrender of Leipzig, three weeks after the battle, was its brilliant result. The city was obliged to clothe the Swedish troops anew, and to purchase an exemption from plunder, by a contribution of 300,000 rix-dollars, to which all the foreign merchants, who had warehouses in the city, were to furnish their quota. In the middle of winter, Torstensohn advanced against Freyberg, and for several weeks defied the inclemency of the season, hoping by his perseverance to weary out the obstinacy of the besieged. But he found that he was merely sacrificing the lives of his soldiers; and at last, the approach of the imperial general, Piccolomini, compelled him, with his weakened army, to retire. He considered it, however, as equivalent to a victory, to have disturbed the repose of the enemy in their winter quarters, who, by the severity of the weather, sustained a loss of 3000 horses. He now made a movement towards the Oder, as if with the view of reinforcing himself with the garrisons of Pomerania and Silesia; but, with the rapidity of lightning, he again appeared upon the Bohemian frontier, penetrated through that kingdom, and relieved Olmutz in Moravia, which was hard pressed by the Imperialists. His camp at Dobitschau, two miles from Olmutz, commanded the whole of Moravia, on which he levied heavy contributions, and carried his ravages almost to the gates of Vienna. In vain did the Emperor attempt to arm the Hungarian nobility in defence of this province; they appealed to their privileges, and refused to serve beyond the limits of their own country. Thus, the time that should have been spent in active resistance, was lost in fruitless negociation, and the entire province was abandoned to the ravages of the Swedes.

While Torstensohn, by his marches and his victories, astonished friend and foe, the armies of the allies had not been inactive in other parts of the empire. The troops of Hesse, under Count Eberstein, and those of Weimar, under Mareschal de Guebriant, had fallen into the Electorate of Cologne, in order to take up their winter quarters there. To get rid of these troublesome guests, the Elector called to his assistance the imperial general Hatzfeldt, and assembled his own troops under General Lamboy. The latter was attacked by the allies in January, 1642, and in a decisive action near Kempen, defeated, with the loss of about 2000 men killed, and about twice as many prisoners. This important victory opened to them the whole Electorate and neighbouring territories, so that the allies were not only enabled to maintain their winter quarters there, but drew from the country large supplies of men and horses.

Guebriant left the Hessians to defend their conquests on the Lower Rhine against Hatzfeldt, and advanced towards Thuringia, as if to second the operations of Torstensohn in Saxony. But instead of joining the Swedes, he soon hurried back to the Rhine and the Maine, from which he seemed to think he had removed farther than was expedient. But being anticipated in the Margraviate of Baden, by the Bavarians under Mercy and John de Werth, he was obliged to wander about for several weeks, exposed, without shelter, to the inclemency of the winter, and generally encamping upon the snow, till he found a miserable refuge in Breisgau. He at last took the field; and, in the next summer, by keeping the Bavarian army employed in Suabia, prevented it from relieving Thionville, which was besieged by Conde. But the superiority of the enemy soon drove him back to Alsace, where he awaited a reinforcement.

The death of Cardinal Richelieu took place in November, 1642, and the subsequent change in the throne and in the ministry, occasioned by the death of Louis XIII., had for some time withdrawn the attention of France from the German war, and was the cause of the inaction of its troops in the field. But Mazarin, the inheritor, not only of Richelieu's power, but also of his principles and his projects, followed out with renewed zeal the plans of his predecessor, though the French subject was destined to pay dearly enough for the political greatness of his country. The main strength of its armies, which Richelieu had employed against the Spaniards, was by Mazarin directed against the Emperor; and the anxiety with which he carried on the war in Germany, proved the sincerity of his opinion, that the German army was the right arm of his king, and a wall of safety around France. Immediately upon the surrender of Thionville, he sent a considerable reinforcement to Field-Marshal Guebriant in Alsace; and to encourage the troops to bear the fatigues of the German war, the celebrated victor of Rocroi, the Duke of Enghien, afterwards Prince of Conde, was placed at their head. Guebriant now felt himself strong enough to appear again in Germany with repute. He hastened across the Rhine with the view of procuring better winter quarters in Suabia, and actually made himself master of Rothweil, where a Bavarian magazine fell into his hands. But the place was too dearly purchased for its worth, and was again lost even more speedily than it had been taken. Guebriant received a wound in the arm, which the surgeon's unskilfulness rendered mortal, and the extent of his loss was felt on the very day of his death.