After serving the German Emperor Charles VI in a campaign against the Ottoman Empire in 1717, he went to Paris to study mathematics, and in 1720 obtained a commission as "maréchal de camp". In 1725, he entered negotiations for election as Duke of Courland, at the insistence of the Duchess Anna Ivanovna, who offered him her hand. He was chosen Duke in 1726, but declined marriage with the duchess. He soon found it impossible to resist her opposition to his claims, but with the assistance of £30,000 lent him by the French actress Adrienne Lecouvreur, he raised a force by which he maintained his authority till 1727, when he withdrew and took up residence in Paris. Lecouvreur was to die mysteriously shortly afterwards: there is controversy as to whether or not she was poisoned by her rival, Maria Karolina Sobieska, Duchess of Bouillon.