This resolution, and the assistance which he immediately despatched to the Emperor in Bohemia, threatened materially to injure the Swedes, and Wrangel was compelled in haste to evacuate that kingdom. He retired through Thuringia into Westphalia and Lunenburg, in the hope of forming a junction with the French army under Turenne, while the Imperial and Bavarian army followed him to the Weser, under Melander and Gronsfeld. His ruin was inevitable, if the enemy should overtake him before his junction with Turenne; but the same consideration which had just saved the Emperor, now proved the salvation of the Swedes. Even amidst all the fury of the conquest, cold calculations of prudence guided the course of the war, and the vigilance of the different courts increased, as the prospect of peace approached. The Elector of Bavaria could not allow the Emperor to obtain so decisive a preponderance as, by the sudden alteration of affairs, might delay the chances of a general peace. Every change of fortune was important now, when a pacification was so ardently desired by all, and when the disturbance of the balance of power among the contracting parties might at once annihilate the work of years, destroy the fruit of long and tedious negociations, and indefinitely protract the repose of Europe. If France sought to restrain the Swedish crown within due bounds, and measured out her assistance according to her successes and defeats, the Elector of Bavaria silently undertook the same task with the Emperor his ally, and determined, by prudently dealing out his aid, to hold the fate of Austria in his own hands. And now that the power of the Emperor threatened once more to attain a dangerous superiority, Maximilian at once ceased to pursue the Swedes. He was also afraid of reprisals from France, who had threatened to direct Turenne's whole force against him if he allowed his troops to cross the Weser. Melander, prevented by the Bavarians from further pursuing Wrangel, crossed by Jena and Erfurt into Hesse, and now appeared as a dangerous enemy in the country which he had formerly defended. If it was the desire of revenge upon his former sovereign, which led him to choose Hesse for the scene of his ravage, he certainly had his full gratification. Under this scourge, the miseries of that unfortunate state reached their height. But he had soon reason to regret that, in the choice of his quarters, he had listened to the dictates of revenge rather than of prudence. In this exhausted country, his army was oppressed by want, while Wrangel was recruiting his strength, and remounting his cavalry in Lunenburg. Too weak to maintain his wretched quarters against the Swedish general, when he opened the campaign in the winter of 1648, and marched against Hesse, he was obliged to retire with disgrace, and take refuge on the banks of the Danube.