When French troops occupied the Duchy of Saxe-Coburg in 1806 during the Napoleonic Wars, Leopold went to Paris where he became part of the Imperial Court of Napoleon. Napoleon offered him the position of adjutant, but Leopold refused. Instead, he went to Russia to take up a military career in the Imperial Russian cavalry, which was at war with France at the time. He campaigned against Napoleon and distinguished himself at the Battle of Kulm at the head of his "cuirassier" division. By 1815, the time of the final defeat of Napoleon, he had reached the rank of lieutenant general at only 25 years of age.