Following the reorganization of the German states during the German mediatization of 1803, the Landgraviate of Hesse-Kassel was raised to the Electorate of Hesse and Landgrave William IX was elevated to Imperial Elector, taking the title William I, Elector of Hesse.
William's grandson, Elector Frederick William, sided with the Austrian Empire in the Austro-Prussian War.