World War 1 was caused by the complex interplay of several factors in Europe including militarism, imperialism, nationalism, and a system of alliances that drew the major European powers into war. Tensions had been rising for decades due to competition for power and colonies, culminating in the assassination of Archduke Franz Ferdinand of Austria-Hungary by Serbian nationalists in June 1914. This triggered a series of diplomatic and military events that led major European powers to declare war on each other over the following month.