Wallenstein now began to assume the title of generalissimo of the Emperor by sea and land. Wismar was taken, and a firm footing gained on the Baltic. Ships were required from Poland and the Hanse towns to carry the war to the other side of the Baltic; to pursue the Danes into the heart of their own country, and to compel them to a peace which might prepare the way to more important conquests. The communication between the Lower German States and the Northern powers would be broken, could the Emperor place himself between them, and encompass Germany, from the Adriatic to the Sound, (the intervening kingdom of Poland being already dependent on him,) with an unbroken line of territory. If such was the Emperor's plan, Wallenstein had a peculiar interest in its execution. These possessions on the Baltic should, he intended, form the first foundation of a power, which had long been the object of his ambition, and which should enable him to throw off his dependence on the Emperor.
To effect this object, it was of extreme importance to gain possession of Stralsund, a town on the Baltic. Its excellent harbour, and the short passage from it to the Swedish and Danish coasts, peculiarly fitted it for a naval station in a war with these powers. This town, the sixth of the Hanseatic League, enjoyed great privileges under the Duke of Pomerania, and totally independent of Denmark, had taken no share in the war. But neither its neutrality, nor its privileges, could protect it against the encroachments of Wallenstein, when he had once cast a longing look upon it.
The request he made, that Stralsund should receive an imperial garrison, had been firmly and honourably rejected by the magistracy, who also refused his cunningly demanded permission to march his troops through the town, Wallenstein, therefore, now proposed to besiege it.
The independence of Stralsund, as securing the free navigation of the Baltic, was equally important to the two Northern kings. A common danger overcame at last the private jealousies which had long divided these princes. In a treaty concluded at Copenhagen in 1628, they bound themselves to assist Stralsund with their combined force, and to oppose in common every foreign power which should appear in the Baltic with hostile views. Christian IV. also threw a sufficient garrison into Stralsund, and by his personal presence animated the courage of the citizens. Some ships of war which Sigismund, King of Poland, had sent to the assistance of the imperial general, were sunk by the Danish fleet; and as Lubeck refused him the use of its shipping, this imperial generalissimo of the sea had not even ships enough to blockade this single harbour.
Nothing could appear more adventurous than to attempt the conquest of a strongly fortified seaport without first blockading its harbour. Wallenstein, however, who as yet had never experienced a check, wished to conquer nature itself, and to perform impossibilities. Stralsund, open to the sea, continued to be supplied with provisions and reinforcements; yet Wallenstein maintained his blockade on the land side, and endeavoured, by boasting menaces, to supply his want of real strength. "I will take this town," said he, "though it were fastened by a chain to the heavens." The Emperor himself, who might have cause to regret an enterprise which promised no very glorious result, joyfully availed himself of the apparent submission and acceptable propositions of the inhabitants, to order the general to retire from the town. Wallenstein despised the command, and continued to harass the besieged by incessant assaults. As the Danish garrison, already much reduced, was unequal to the fatigues of this prolonged defence, and the king was unable to detach any further troops to their support, Stralsund, with Christian's consent, threw itself under the protection of the King of Sweden. The Danish commander left the town to make way for a Swedish governor, who gloriously defended it. Here Wallenstein's good fortune forsook him; and, for the first time, his pride experienced the humiliation of relinquishing his prey, after the loss of many months and of 12,000 men. The necessity to which he reduced the town of applying for protection to Sweden, laid the foundation of a close alliance between Gustavus Adolphus and Stralsund, which greatly facilitated the entrance of the Swedes into Germany.
Hitherto invariable success had attended the arms of the Emperor and the League, and Christian IV., defeated in Germany, had sought refuge in his own islands; but the Baltic checked the further progress of the conquerors. The want of ships not only stopped the pursuit of the king, but endangered their previous acquisitions. The union of the two northern monarchs was most to be dreaded, because, so long as it lasted, it effectually prevented the Emperor and his general from acquiring a footing on the Baltic, or effecting a landing in Sweden. But if they could succeed in dissolving this union, and especially securing the friendship of the Danish king, they might hope to overpower the insulated force of Sweden. The dread of the interference of foreign powers, the insubordination of the Protestants in his own states, and still more the storm which was gradually darkening along the whole of Protestant Germany, inclined the Emperor to peace, which his general, from opposite motives, was equally desirous to effect. Far from wishing for a state of things which would reduce him from the meridian of greatness and glory to the obscurity of private life, he only wished to change the theatre of war, and by a partial peace to prolong the general confusion. The friendship of Denmark, whose neighbour he had become as Duke of Mecklenburgh, was most important for the success of his ambitious views; and he resolved, even at the sacrifice of his sovereign's interests, to secure its alliance.
By the treaty of Copenhagen, Christian IV. had expressly engaged not to conclude a separate peace with the Emperor, without the consent of Sweden. Notwithstanding, Wallenstein's proposition was readily received by him. In a conference at Lubeck in 1629, from which Wallenstein, with studied contempt, excluded the Swedish ambassadors who came to intercede for Mecklenburgh, all the conquests taken by the imperialists were restored to the Danes. The conditions imposed upon the king were, that he should interfere no farther with the affairs of Germany than was called for by his character of Duke of Holstein; that he should on no pretext harass the Chapters of Lower Germany, and should leave the Dukes of Mecklenburgh to their fate. By Christian himself had these princes been involved in the war with the Emperor; he now sacrificed them, to gain the favour of the usurper of their territories. Among the motives which had engaged him in a war with the Emperor, not the least was the restoration of his relation, the Elector Palatine—yet the name of that unfortunate prince was not even mentioned in the treaty; while in one of its articles the legitimacy of the Bavarian election was expressly recognised. Thus meanly and ingloriously did Christian IV. retire from the field.
Ferdinand had it now in his power, for the second time, to secure the tranquillity of Germany; and it depended solely on his will whether the treaty with Denmark should or should not be the basis of a general peace. From every quarter arose the cry of the unfortunate, petitioning for an end of their sufferings; the cruelties of his soldiers, and the rapacity of his generals, had exceeded all bounds. Germany, laid waste by the desolating bands of Mansfeld and the Duke of Brunswick, and by the still more terrible hordes of Tilly and Wallenstein, lay exhausted, bleeding, wasted, and sighing for repose. An anxious desire for peace was felt by all conditions, and by the Emperor himself; involved as he was in a war with France in Upper Italy, exhausted by his past warfare in Germany, and apprehensive of the day of reckoning which was approaching. But, unfortunately, the conditions on which alone the two religious parties were willing respectively to sheath the sword, were irreconcileable. The Roman Catholics wished to terminate the war to their own advantage; the Protestants advanced equal pretensions. The Emperor, instead of uniting both parties by a prudent moderation, sided with one; and thus Germany was again plunged in the horrors of a bloody war.
From the very close of the Bohemian troubles, Ferdinand had carried on a counter reformation in his hereditary dominions, in which, however, from regard to some of the Protestant Estates, he proceeded, at first, with moderation. But the victories of his generals in Lower Germany encouraged him to throw off all reserve. Accordingly he had it intimated to all the Protestants in these dominions, that they must either abandon their religion, or their native country,—a bitter and dreadful alternative, which excited the most violent commotions among his Austrian subjects. In the Palatinate, immediately after the expulsion of Frederick, the Protestant religion had been suppressed, and its professors expelled from the University of Heidelberg.
All this was but the prelude to greater changes. In the Electoral Congress held at Muehlhausen, the Roman Catholics had demanded of the Emperor that all the archbishoprics, bishoprics, mediate and immediate, abbacies and monasteries, which, since the Diet of Augsburg, had been secularized by the Protestants, should be restored to the church, in order to indemnify them for the losses and sufferings in the war. To a Roman Catholic prince so zealous as Ferdinand was, such a hint was not likely to be neglected; but he still thought it would be premature to arouse the whole Protestants of Germany by so decisive a step. Not a single Protestant prince but would be deprived, by this revocation of the religious foundations, of a part of his lands; for where these revenues had not actually been diverted to secular purposes they had been made over to the Protestant church. To this source, many princes owed the chief part of their revenues and importance. All, without exception, would be irritated by this demand for restoration. The religious treaty did not expressly deny their right to these chapters, although it did not allow it. But a possession which had now been held for nearly a century, the silence of four preceding emperors, and the law of equity, which gave them an equal right with the Roman Catholics to the foundations of their common ancestors, might be strongly pleaded by them as a valid title. Besides the actual loss of power and authority, which the surrender of these foundations would occasion, besides the inevitable confusion which would necessarily attend it, one important disadvantage to which it would lead, was, that the restoration of the Roman Catholic bishops would increase the strength of that party in the Diet by so many additional votes. Such grievous sacrifices likely to fall on the Protestants, made the Emperor apprehensive of a formidable opposition; and until the military ardour should have cooled in Germany, he had no wish to provoke a party formidable by its union, and which in the Elector of Saxony had a powerful leader. He resolved, therefore, to try the experiment at first on a small scale, in order to ascertain how it was likely to succeed on a larger one. Accordingly, some of the free cities in Upper Germany, and the Duke of Wirtemberg, received orders to surrender to the Roman Catholics several of the confiscated chapters.