Determination of borders between the new countries was complex and difficult, and not always peaceful: While the northeastern border with the Kingdom of Italy along the "Julian March" was already determined by the 1915 Treaty of London, the demarcation line between Yugoslavia and the rump state of German-Austria was a difficult and highly disputed matter. The principle of self-determination, championed by U.S. President Woodrow Wilson, was taken up by both Slovenes and German-Austrians in the Carinthian, Styrian and Carniolan lands of the defunct Habsburg empire. The rising tensions culminated in clashes of arms, as on Marburg's Bloody Sunday in Lower Styria and the continued fighting of paramilitary groups in southeastern Carinthia.