In the next year the tide of victory rolled on. Wallenstein, now made duke of Friedland, marched into Silesia with irresistible forces, and sent fifty standards to Vienna as evidence of his conquest. Then, joining hands with Tilly on the lower Elbe, the united armies poured into Holstein, and overran Denmark until stopped by the sea, and forced the unfortunate Christian to take refuge in the islands. In February 1628, Ferdinand, following the precedent of the Elector Palatine, put the dukes of Mecklenberg to the ban for the assistance they had given to Christian, declared their lands forfeited, and authorised Wallenstein to occupy and administer them in pledge for the expenses incurred. Sweeping over the country the imperial general seized upon the ports of Wismar and Rostock, obliged the duke of Pomerania to put the long coast line of his duchy under the care of the imperial troops, and was only checked in his career of conquest in March 1628 by the marshes and the fortifications of Stralsund. [Sidenote: =Siege of Stralsund, 1628.=] For five long months the imperialist army lay before the city, attempting the almost impossible feat of the capture of a defended city open to the sea by an attack from the land side only, for none knew better than Wallenstein himself the importance of the issue. All the southern coast of the Baltic from Dantzig to Lübeck, except Stralsund, owned his authority. Across the water lay the only foe he had now to fear. Sovereignty over the Baltic as well as over the Baltic provinces was necessary to him if he was to be safe from the attacks of Sweden. To further this policy, he had already obtained from the Emperor the title of admiral of the Baltic, and he was negotiating with the Hanse towns to provide him with a fleet, which should make the title something of a reality. As long as Stralsund afforded to the enemy an open door into the heart of Germany, the first steps necessary to gain that sovereignty were not complete. Nor was that all. Hitherto the opposition to the Emperor in Germany had been led by furious partisans like Christian of Anhalt, military adventurers like Mansfeld and Christian of Brunswick, or self-seeking politicians like Christian of Denmark and the other holders of the ecclesiastical lands. The German people and the cities of Germany had, as a rule, kept themselves aloof from the struggle, or extended their sympathies to the Emperor as the representative of order. But the siege of Stralsund showed that new forces were coming into play. It was the citizens, not their leaders, who insisted on fighting to the last gasp. The independent spirit of civic liberty was determined not to submit to a military dictatorship. The religious spirit of staunch Protestantism was determined not to make terms with the victorious Counter-Reformation. When Wallenstein, foiled and exasperated, drew off his army on August 3d from before the walls of Stralsund, he at least understood that among the cities of