Upper Styria
On the collapse of Austria-Hungary in the aftermath of World War I, the rump state of German Austria claimed all Cisleithanian Austria with a significant German-speaking population including large parts of the Styrian duchy, while the Slovene Lower Styrian part joined the State of Slovenes, Croats and Serbs. Armed conflicts arose especially around the multilingual town of Maribor (Marburg), until by the 1919 Treaty of St Germain the former duchy was partitioned broadly along ethnic lines, with two thirds of its territory (then called Upper Styria) including the ducal capital of Graz remaining with Austria, and the southern third of Lower Styria with Maribor passing to the Kingdom of Serbs, Croats and Slovenes, eventually becoming part of modern Slovenia.