The causes of World War I, which began in central Europe in late June 1914, included intertwined factors, such as the conflicts and hostility of the four decades leading up to the war. Militarism, alliances, imperialism, and nationalism played major roles in the conflict as well. The immediate origins of the war, however, lay in the decisions taken by statesmen and generals during the Crisis of 1914, casus belli for which was the assassination of Archduke Franz Ferdinand of Austria and his wife by Gavrilo Princip, an irredentist Serb.
The crisis came after a long and difficult series of diplomatic clashes between the Great Powers (Italy, France, Germany, the British Empire, Austria-Hungarian Empire and Russia) over European and colonial issues in the decade before 1914 that had left tensions high. In turn these diplomatic clashes can be traced to changes in the balance of power in Europe since 1867. The more immediate cause for the war was tensions over territory in the Balkans. Austria-Hungary competed with Serbia and Russia for territory and influence in the region and they pulled the rest of the Great Powers into the conflict through their various alliances and treaties.
The topic of the causes of World War I is one of the most studied in all of world history. Scholars have differed significantly in their interpretations of the event.