During the Napoleonic reorganisation of the Empire in 1803, the Landgrave of Hesse-Kassel was elevated to an Electorate and Landgrave William IX became an Imperial Elector. Many members of the Hesse-Kassel House served in the Danish military gaining high ranks and power in the Oldenburg realm due to the fact that many Landgraves were married to Danish princesses. Members of the family who are known to have served Denmark-Norway include Prince Frederik of Hesse-Kassel, Prince Frederick of Hesse-Kassel, and Prince Charles of Hesse-Kassel. It was later occupied by French troops and became part of the Kingdom of Westphalia, a French satellite state. The Electorate of Hesse was restored at the end of the Napoleonic Wars, though by that time there was no longer an emperor to elect.