He went into Spanish service by 1614 at the latest and fought under
Spinola in the
Palatinate and the Netherlands. After the
Eighty Years' War broke out again, he took part in the
siege of Jülich (1621–1622). During the
siege of Breda in 1625 he commanded one of the four camps near the city. He is also shown behind Spinola in the well-known picture by
Velasquez. In 1628 he received the
Order of the Golden Fleece from
king Philip IV. At the beginning of 1633, as general of artillery, he led an advance in support of the Elector of Cologne, Ferdinand, against the Swedes. He captured
Nonnenwerth,
Olbrück Castle,
Saffenburg Castle and
Landskron Castle on the Rhine and along the Ahr. When the Swedes under
Baudissin took
Hammerstein Castle in return and attacked
Remagen, Isenburg moved towards them and pushed them back. In mid-March, however, he had to lift the siege of
Andernach and retreat across the Rhine in the direction of
Linz am Rhein before the Swedish relief army led by Baudissin's successor,
Christian I, Count Palatine of Birkenfeld-Bischweiler. In 1636 the king appointed him governor and governor-general of the provinces of
Namur and
Artois. In August of that year he took the border town of
Hirson. In 1638 he took part in the successful relief of the besieged
St. Omer under
Prince Thomas of Savoy and
Ottavio Piccolomini. In 1643 he besieged the fortress of
Rocroi on the French border.
Francisco de Melo wanted to come to his aid, but then met a relief army under
Louis de Bourbon. It came to the Battle of Rocroi, which ended in a heavy Spanish defeat. Isenburg survived the battle but retired from military life afterwards. He succeeded
Count von Fontaine as Generalfeldmeister of the Flemish army, since he fell in battle. On 29 September 1645 he was also appointed head of finances (grand treasurer) of the Netherlands, the tax administration of the king of Spain. Isenburg lived in Brussels, where he also died, his county was looked after by administrators. His tomb is in the
Cathedral of St. Michael and St. Gudula. == References ==