But the Imperialists, under the command of Gallas, entered that duchy at Ribses, and overran it by their superior strength. Usedom and Wolgast were taken by storm, Demmin capitulated, and the Swedes were driven far into Lower Pomerania. It was, too, more important for them at this moment than ever, to maintain a footing in that country, for Bogislaus XIV. had died that year, and Sweden must prepare to establish its title to Pomerania. To prevent the Elector of Brandenburg from making good the title to that duchy, which the treaty of Prague had given him, Sweden exerted her utmost energies, and supported its generals to the extent of her ability, both with troops and money. In other quarters of the kingdom, the affairs of the Swedes began to wear a more favourable aspect, and to recover from the humiliation into which they had been thrown by the inaction of France, and the desertion of their allies. For, after their hasty retreat into Pomerania, they had lost one place after another in Upper Saxony; the princes of Mecklenburg, closely pressed by the troops of the Emperor, began to lean to the side of Austria, and even George, Duke of Lunenburg, declared against them. Ehrenbreitstein was starved into a surrender by the Bavarian General de Werth, and the Austrians possessed themselves of all the works which had been thrown up on the Rhine. France had been the sufferer in the contest with Spain; and the event had by no means justified the pompous expectations which had accompanied the opening of the campaign. Every place which the Swedes had held in the interior of Germany was lost; and only the principal towns in Pomerania still remained in their hands. But a single campaign raised them from this state of humiliation; and the vigorous diversion, which the victorious Bernard had effected upon the Rhine, gave quite a new turn to affairs.
The misunderstandings between France and Sweden were now at last adjusted, and the old treaty between these powers confirmed at Hamburg, with fresh advantages for Sweden. In Hesse, the politic Landgravine Amelia had, with the approbation of the Estates, assumed the government after the death of her husband, and resolutely maintained her rights against the Emperor and the House of Darmstadt. Already zealously attached to the Swedish Protestant party, on religious grounds, she only awaited a favourable opportunity openly to declare herself. By artful delays, and by prolonging the negociations with the Emperor, she had succeeded in keeping him inactive, till she had concluded a secret compact with France, and the victories of Duke Bernard had given a favourable turn to the affairs of the Protestants. She now at once threw off the mask, and renewed her former alliance with the Swedish crown. The Electoral Prince of the Palatinate was also stimulated, by the success of Bernard, to try his fortune against the common enemy. Raising troops in Holland with English money, he formed a magazine at Meppen, and joined the Swedes in Westphalia. His magazine was, however, quickly lost; his army defeated near Flotha, by Count Hatzfeld; but his attempt served to occupy for some time the attention of the enemy, and thereby facilitated the operations of the Swedes in other quarters. Other friends began to appear, as fortune declared in their favour, and the circumstance, that the States of Lower Saxony embraced a neutrality, was of itself no inconsiderable advantage.
Under these advantages, and reinforced by 14,000 fresh troops from Sweden and Livonia. Banner opened, with the most favourable prospects, the campaign of 1638. The Imperialists who were in possession of Upper Pomerania and Mecklenburg, either abandoned their positions, or deserted in crowds to the Swedes, to avoid the horrors of famine, the most formidable enemy in this exhausted country. The whole country betwixt the Elbe and the Oder was so desolated by the past marchings and quarterings of the troops, that, in order to support his army on its march into Saxony and Bohemia, Banner was obliged to take a circuitous route from Lower Pomerania into Lower Saxony, and then into the Electorate of Saxony through the territory of Halberstadt. The impatience of the Lower Saxon States to get rid of such troublesome guests, procured him so plentiful a supply of provisions, that he was provided with bread in Magdeburg itself, where famine had even overcome the natural antipathy of men to human flesh. His approach spread consternation among the Saxons; but his views were directed not against this exhausted country, but against the hereditary dominions of the Emperor. The victories of Bernard encouraged him, while the prosperity of the Austrian provinces excited his hopes of booty. After defeating the Imperial General Salis, at Elsterberg, totally routing the Saxon army at Chemnitz, and taking Pirna, he penetrated with irresistible impetuosity into Bohemia, crossed the Elbe, threatened Prague, took Brandeis and Leutmeritz, defeated General Hofkirchen with ten regiments, and spread terror and devastation through that defenceless kingdom. Booty was his sole object, and whatever he could not carry off he destroyed. In order to remove more of the corn, the ears were cut from the stalks, and the latter burnt. Above a thousand castles, hamlets, and villages were laid in ashes; sometimes more than a hundred were seen burning in one night. From Bohemia he crossed into Silesia, and it was his intention to carry his ravages even into Moravia and Austria. But to prevent this, Count Hatzfeld was summoned from Westphalia, and Piccolomini from the Netherlands, to hasten with all speed to this quarter. The Archduke Leopold, brother to the Emperor, assumed the command, in order to repair the errors of his predecessor Gallas, and to raise the army from the low ebb to which it had fallen.
The result justified the change, and the campaign of 1640 appeared to take a most unfortunate turn for the Swedes. They were successively driven out of all their posts in Bohemia, and anxious only to secure their plunder, they precipitately crossed the heights of Meissen. But being followed into Saxony by the pursuing enemy, and defeated at Plauen, they were obliged to take refuge in Thuringia. Made masters of the field in a single summer, they were as rapidly dispossessed; but only to acquire it a second time, and to hurry from one extreme to another. The army of Banner, weakened and on the brink of destruction in its camp at Erfurt, suddenly recovered itself. The Duke of Lunenburg abandoned the treaty of Prague, and joined Banner with the very troops which, the year before, had fought against him. Hesse Cassel sent reinforcements, and the Duke of Longueville came to his support with the army of the late Duke Bernard. Once more numerically superior to the Imperialists, Banner offered them battle near Saalfeld; but their leader, Piccolomini, prudently declined an engagement, having chosen too strong a position to be forced. When the Bavarians at length separated from the Imperialists, and marched towards Franconia, Banner attempted an attack upon this divided corps, but the attempt was frustrated by the skill of the Bavarian General Von Mercy, and the near approach of the main body of the Imperialists. Both armies now moved into the exhausted territory of Hesse, where they formed intrenched camps near each other, till at last famine and the severity of the winter compelled them both to retire. Piccolomini chose the fertile banks of the Weser for his winter quarters; but being outflanked by Banner, he was obliged to give way to the Swedes, and to impose on the Franconian sees the burden of maintaining his army.