von Kruse organized the military of the state of Nassau during the Napoleonic Wars, and participated in the lengthy French campaign in the Iberian Peninsula; under secret orders from his Duke, he switched sides in 1814, and fought against the French in northern Europe. He commanded the Nassau infantry brigade at the Battle of Waterloo. In his retirement, he experimented in new farming and cattle breeding techniques on a small acreage given to him by the Duke of Nassau, exploring the problems in raising healthy cattle.