Yugoslavism refers to nationalism or patriotism centred upon the Yugoslavs - an identity referring to a united singular South Slav people and the South Slav populated territories of southeastern Europe. Yugoslavism has historically advocated the union of all South Slav populated territories now composing Bosnia and Herzegovina, Bulgaria, Croatia, Montenegro, Serbia (and the disputed region of Kosovo), Slovenia, and Macedonia. Yugoslavism was a potent political force during World War I with the assassination of Austrian Archduke Franz Ferdinand by the Yugoslavist militant Gavrilo Princip and the subsequent invasion of Serbia by Austria-Hungary, which sought to rally the South Slav peoples against Austro-Hungarian imperial domination and in support of an independent Yugoslavia that was achieved in 1918.