Roman Catholic mercenary who fought for the Protestant cause during the Thirty Years War (1618-48). He was the Catholic League´s most dangerous opponent until his early death in 1626.
An illegitimate son of Peter Ernst, Fürst von Mansfeld governor of the Spanish fortress in Luxembourg he entered the Habsburg army and fought in much of Europe. Although he was legitimized, the stigma of his birth adversely influenced his career and during the first decade of 17th century he gradually became an enemy of the House of Austria.
At the outbreak of the Thirty Years War (1618) he was in the service of the Protestant Union and campaigning against the Habsburgs in Bohemia captured Plzen (Pilsen).
He neverthless failed support the new Protestant Bohemian king namely the elector Palatine Frederick V who was subsequently defeated at the Battle of White Mountain (November 1620). For the next two years he successful defended the Elector´s Rhenish provinces against Gen. Johann Tserclaes, Graf von Tilly, commanding the Catholic forces.
By 1623 Frederick V´s treasury was exhausted. After futile negotiations with Austria and the French Huguenots, Mansfeld and his ally, Christian of Brunswick marched through Lorraine and Flanders to enter the service of the United Provinces of the Netherlands conquering and holding East Frisia until 1624.
Mansfeld then acquired English subsidies for the entry of Denmark into the war. While Christian IV of Denmark fought Tilly in Lower Sexony he opposed the imperial general Albrecht von Wallenstein at Dessau but was unable to dislodge him. Followed by Wallenstein he the marched to Hungary with a new army in French pay to join forces with Prince Gábor Bethlen of Transylvania who was fighting the Austrians in the Balkans.
Epidemics caused considerable loss to both sides and after Gábor Bethlen negotiated separately with Austria he decided to enter the Venetian service. He died on his way toward Venetian territory.