About 1624 he paid three visits to London, where he was hailed as a hero by the populace, and at least one to Paris. James I, being the father-in-law of Frederick V, Elector Palatine, was anxious to furnish him with men and money for the recovery of the Palatinate, but it was not until January 1625 that Mansfeld and his army of "raw and poor rascals" sailed from Dover to the Netherlands before failing to relieve the siege of Breda. Later in the year, the Thirty Years' War having been renewed under the leadership of Christian IV of Denmark, he re-entered Germany to take part therein but on 25 April 1626 Wallenstein inflicted a severe defeat upon him at the bridge of Dessau. Mansfeld, however, quickly raised another army, with which he intended to attack the hereditary lands of the house of Austria, and pursued by Wallenstein he pressed forward towards Hungary, where he hoped to accomplish his purpose by the aid of Bethlen Gábor, prince of Transylvania but when Bethlen changed his policy and made peace with the emperor, Mansfeld was compelled to disband his troops. He set out for Venice, but when he reached Rakovica near Sarajevo, in Bosnia, he was taken ill, and here he died on 29 November 1626, probably from a hemorrhage. He was buried at Split.