Some scholars identify nationalism as a major trigger for World War I; the act of assassination against Archduke Ferdinand was an act of nationalist protest by Serbians who opposed Austrian presence in their lands. Austria declared war as a result of this action, kicking off the conflict that grew into the first World War. This nationalism is contrasted by the imperialism that was taking place at the hands of European nations such as Austria within Europe, including Serbia and the Balkans.
Although World War I involved many more nations and included a variety of other conflicts than an fight between the Austrian government and Serbian nationals, ultimately, this was a war that was kicked off by the radical act of a Serbian nationalist. For example, the United States, Germany, France and Great Britain, including the British territories of Australia and Canada, were all involved with what started as a regional conflict between a nationalist group fighting against the occupying forces of an imperialist government. Arguably, though, nationalist sentiment in other European countries was an undercurrent of the war in general. For example, nationalist sentiment in Germany has been identified as a source of tension between that nation and other European countries, such as Great Britain.