By 1625 Wallenstein had not only reached the rank of general, but Ferdinand II had also given him the title of Duke of Friedland. This was the time of the Thirty Years' War, and Wallenstein was active in recruiting men and raising an army which he led into battle in both Bohemia and Germany. His army was victorious over the Danes during the Danish war (1625-1629).

Wallenstein was an ambitious man who thought that he had an important political role to play in an empire which, he believed, would eventually include the whole of Western Europe and the lands controlled by the Turks. Ferdinand II was wary of Wallenstein's ambition and, in 1630, he dismissed him as commander of his armies. By 1632, however, Ferdinand was forced to reinstate his general. The Swedish king, Gustavus II and his Protestant army had invaded Germany two years earlier and were still within the borders of the empire. Gustavus had already defeated the Imperial army at Breitenfield in 1631, and, one year later, he assembled his troops against Wallenstein's. The resulting battle of Lützen was another Swedish victory, although Gustavus was killed in combat.

In 1633, Wallenstein made his move into the political scene when he attempted to arbitrate between the Swedish and German Protestant leaders and the Holy Roman Empire after his victory at Steinan in Silesia. Unfortunately, there were certain Catholic princes who were already jealous of Wallenstein's ability and power. They were not about to see Wallenstein succeed in the political arena and proceeded to poison the Emperor's mind against his general. Convinced by then that Wallenstein was a traitor, in 1634 Ferdinand ordered his arrest. Wallenstein was murdered as he tried to escape from the arresting officers.