Turenne then marched towards the Maine, and, halting ten leagues from Mayence, sent for the infantry, of which he had left a portion there, to join him.  The whole force of the allies was now united, and took many towns.  As, however, they were still inferior in force to the Imperialists, Turenne refused to weaken himself by placing garrisons in these places, contenting himself with blowing up the fortifications of some and carrying off the principal inhabitants of others as hostages.  The Imperialist army still remained inactive, and Turenne was able therefore to turn his attention to Bavaria.  Crossing the Rhine at Donauwurth he besieged Augsburg and Rain.  The latter place was captured, but the former, being reinforced by fifteen hundred men, held out stoutly, and it was necessary to open trenches and proceed in regular form against it.  The Duke of Bavaria, greatly alarmed at this invasion of his dominions, sent off message after message to the emperor, complaining of the manner in which the Imperial army remained inactive, leaving the allies to employ their whole force against him.  He threatened that unless the army advanced at once to his assistance he would make terms with France.  Imperative orders were thereupon sent to the archduke to move against the French.  The allies fell back, as his force was greatly superior to theirs, and the archduke took up a strong position, intending to force the allies to retire into Franconia as soon as the country round them was exhausted.

Turenne and Wrangel divined his purpose, and although it was now the beginning of November and snow was on the ground, they marched against him.  On arriving near his camp they found that it was strongly fortified, and could be attacked only by passing behind great marshes and defiles.  Changing their intentions, they left two thousand horse in front of his camp, making believe that they intended to attack him, then marched with all haste to the Lech and advanced against Landsberg, which they took by assault.  In the city were the principal magazines of the Imperialist army, and the allies, finding sufficient provisions there to last for six months, encamped round the city and decided to winter there unless attacked, in the meantime sending out bodies of cavalry, which levied contributions up to the very gates of Munich.  Leopold, thus deprived of his magazines, retired with the Austrian contingent, and the Bavarians returned home.

The Duke of Bavaria, finding that his whole dominions would be captured unless he made terms, therefore opened negotiations, and on the 14th of March, 1646, peace was signed, the terms being that he should separate himself entirely from the empire and deliver five of his fortresses to the allies, who would thus, should he again break his word, have means of access into his dominions.  The allied forces were now in a condition to march upon Vienna.  They had during the winter plundered a large portion of Bavaria; they and their horses had recovered from their fatigue, and their force now amounted to fourteen thousand foot and twenty thousand horse.  At this moment, when the Imperialists believed that all was lost, for without the assistance of Bavaria they could put no army in the field that could hope to make head against the allies, Mazarin interposed and saved Austria from destruction.