The third period of the war, from 1624 to 1629, is characterized by the intervention of the Powers outside the immediate sphere of German or Imperial interests. France, under Richelieu, became concerned at the growing power of the Hapsburgs, while James I of England began to show anxiety at his son-in-law's adverse fortunes, though without achieving any successful intervention. The chief feature of this campaign was the entry into the field of Christian IV of Denmark with a powerful army to join Mansfeld and Christian of Brunswick in invading the Imperial and Austrian territories. But the savageries and excesses of Mansfeld's troops had disgusted and alienated all sides. It was at this time that Wallenstein, Duke of Friedland, was appointed general of the Imperial troops, and soon after succeeded in completely routing Mansfeld at the battle of Dessau Bridge in 1626. Four months later Tilly completely defeated Christian IV and his Danes at Lutter. Wallenstein, on his side, followed up his success, driving Mansfeld into Hungary. Mansfeld, in spite of some fugitive successes in the Austrian dominions in the course of his retreat, was compelled by Wallenstein to evacuate Hungary, shortly after which he died. The campaign ended with the Peace of Lubeck in 1629. The action of the Emperor Ferdinand in attempting to enforce the restitution of Church lands in North Germany was the proximate cause of the next great campaign, which constitutes the fourth period of the Thirty Years' War (1630-36). The immediate occasion was, however, Wallenstein's seizure of certain towns in Mecklenburg, over which he claimed rights by Imperial grant two years before. This, which may be regarded as the greatest period of the Thirty Years' War, was characterized by the appearance on the scene of Gustavus Adolphus, the Swedish King. He was not in time, however, to prevent the sacking of Magdeburg by the troops of Tilly and Poppenheim. The former, nevertheless, was defeated by the Swedes at the important battle of Breitenfeld in 1631. The following year the Imperial army was again defeated on the Lach. Thereupon Gustavus occupied Muenchen, though he was subsequently compelled by Wallenstein to evacuate the city. The last great victory of Gustavus was at Luetzen in 1632, at which battle the great leader met his death. Wallenstein, who was now in favour of a policy of peace and political reconstruction, was assassinated in 1634 with the connivance of the Emperor. On September 6th of the same year the Protestant army, under Bernhard of Saxe-Weimar, sustained an overwhelming defeat at Noerdlingen, and the Peace of Prague the following year ended the campaign.