Prussian Province of Westphalia but gained territory on the left bank of the Rhine centred on Mainz, which became known as Rhenish Hesse (), and the remainder of Isenburg. Orange-Nassau, whose ruler was now also King William I of the Netherlands and Grand Duke of Luxembourg, was ceded to Prussia but most of its territory aside from Siegen was then ceded on to Nassau. Hesse-Homburg and the Free City of Frankfurt were also restored. While the other former Electors had gained other titles, becoming either Kings or Grand Dukes, the Elector of Hesse-Kassel alone retained the anachronistic title of Prince-Elector; a request to be recognised as "King of the Chatti" () was rejected by the Congress. Following the mediatisations and the Congress of Vienna significantly fewer states remained in the region that is now Hesse: the Hessian states, Nassau, Waldeck and Frankfurt. The Kingdoms of Prussia and Bavaria also held some territory in the region. The Congress also established the German Confederation, of which they all became members. Hesse-Hanau was (re-)absorbed into Hesse-Kassel in 1821. German Empire In the 1866 Austro-Prussian War the states of the region allied with Austria were defeated during the Campaign of the Main. Following Prussia's victory and dissolution of the German Confederation, Prussia annexed Electoral Hesse, Frankfurt, Hesse-Homburg, Nassau and small parts of Bavaria and the Grand Duchy of Hesse, which were then combined into the Province of Hesse-Nassau. The name survived, denoting the region around Kassel. The Grand Duchy of Hesse retained its autonomy in defeat because a greater part of the country was situated south of the river Main and it was feared that Prussian expansion beyond the Main might provoke France. However, Upper Hesse (: the parts of Hesse-Darmstadt north of the Main around the town of Gießen) was incorporated into the North German Confederation (), a tight federation of German states established by Prussia in 1867, while also remaining part of the Grand Duchy. In 1871, after France's defeat in the Franco-Prussian War, the whole of the Grand Duchy joined the German Empire. Around the turn of the 20th century, Darmstadt was one of the centres of the Jugendstil. Until 1907, the Grand Duchy of Hesse used the Hessian red and white lion barry as its coat-of-arms. Weimar and Nazi periods The revolution of 1918 following the German defeat in WWI transformed Hesse-Darmstadt from a monarchy to a republic, which officially