Meanwhile, the war along the Rhine assumed more and more the savage character that made it so destructive to the land. Mansfeld, driven from the Palatinate, supported his ferocious troops almost entirely by plundering. Tilly, the chief general of the Catholic League, followed similar tactics, and, wherever they passed, the land lay ruined behind them. Some of the lesser Protestant princes joined Mansfeld, but Tilly proved a great military leader, and his opponents were slowly crowded back into Northern Germany. The Emperor forced his religion upon the Rhine districts, as he had upon Bohemia and Austria. The Protestant world at last began to take alarm. Both England and Holland lent Mansfeld support. The King of Denmark, drawing as many of the Protestant German princes as possible to his side, joined vigorously in the contest. This Danish struggle may be considered the third period of the war. It lasted from about 1625 to 1629, and introduces one of the two most remarkable men of the period. Albert of Waldstein, or Wallenstein, as he is generally called, was a native of Bohemia, who joined the Catholics, and won military fame and experience fighting on the imperial side in the Bohemian war. He acquired vast wealth through marriage and the purchase of the confiscated Protestant estates. Proving a remarkably capable financial manager, he was soon the richest subject in the empire, and was created Duke of Friedland, a district of Bohemia. All of these successes were to Wallenstein mere preliminary steps to an even more boundless ambition. He studied the political outlook, and his keen eye saw the possibility of vastly expanding Mansfeld's barbaric system of supporting his soldiers by plunder. The Emperor Ferdinand had but few troops of his own, and they were needed for quelling rebellion within his personal domains. For carrying on the war along the Rhine, he was entirely dependent upon the princes of the Catholic League and their army under Tilly. Wallenstein now came forward and offered to supply the Emperor with a powerful imperial army which should not cost him a penny. This offer, coming from a mere private gentleman, sounded absurd; and for a time Wallenstein was put aside with contemptuous laughter. At last the Emperor told him, if he thought he could raise as many as ten thousand men, to go ahead. "If I have only ten thousand," said Wallenstein, "we must accept what people choose to give us. If I have thirty thousand, we can take what we like."