An imperial "generalissimo" by land, and Admiral of the Baltic Sea from 21 April 1628, Wallenstein found himself released from service in 1630 after Ferdinand grew wary of his ambition. Several Protestant victories over Catholic armies induced Ferdinand to recall Wallenstein (Gollersdorf April 1632), who then defeated the Swedish king Gustavus Adolphus at Alte Veste. The Swedish king was later killed at the Battle of Lützen. Wallenstein realised the war could last decades and, during the summer of 1633, arranged a series of armistices to negotiate peace. These proved to be his undoing as plotters accused him of treachery and Emperor Ferdinand II ordered his assassination. Dissatisfied with the Emperor's treatment of him, Wallenstein considered allying with the Protestants. However, he was assassinated at Eger in Bohemia by one of the army's officials, with the emperor's approval.