The causes of World War I remain controversial. World War I began in the Balkans in late July 1914 and ended in November 1918, leaving 17 million dead and 20 million wounded.
Scholars looking at the long-term seek to explain why two rival sets of powers – Germany and Austria-Hungary on the one hand, and Russia, France, and Great Britain on the other – had come into conflict by 1914. They look at such factors as political, territorial and economic conflicts, militarism, a complex web of alliances and alignments, imperialism, the growth of nationalism, and the power vacuum created by the decline of the Ottoman Empire. Other important long-term or structural factors that are often studied include unresolved territorial disputes, the perceived breakdown of the balance of power in Europe, convoluted and fragmented governance, the arms races of the previous decades, and military planning.
Scholars doing short-term analysis focused on the summer of 1914 ask if the conflict could have been stopped, or whether it was out of control. The immediate causes lay in decisions made by statesmen and generals during the July Crisis of 1914. This crisis was triggered by the assassination of Archduke Franz Ferdinand of Austria by the Bosnian-Serb nationalist Gavrilo Princip who had been supported by a nationalist organization in Serbia. The crisis escalated as the conflict between Austria-Hungary and Serbia came to involve Russia, Germany, France, and ultimately Belgium and Great Britain. Other factors that came into play during the diplomatic crisis that preceded the war included misperceptions of intent (e.g., the German belief that Britain would remain neutral), fatalism that war was inevitable, and the speed of the crisis, which was exacerbated by delays and misunderstandings in diplomatic communications.
The crisis followed a series of diplomatic clashes among the Great Powers (Italy, France, Germany, Britain, Austria-Hungary and Russia) over European and colonial issues in the decades before 1914 that had left tensions high. In turn, these public clashes can be traced to changes in the balance of power in Europe since 1867.
Consensus on the origins of the war remains elusive since historians disagree on key factors, and place differing emphasis on a variety of factors. This is compounded by changing historical arguments over time, particularly the delayed availability of classified historical archives. The deepest distinction among historians is between those who focus on the actions of Germany and Austria-Hungary as key and those who focus on a wider group of actors. Secondary fault lines exist between those who believe that Germany deliberately planned a European war, those who believe that the war was ultimately unplanned but still caused principally by Germany and Austria-Hungary taking risks, and those who believe that either all or some of the other powers, namely Russia, France, Serbia and Great Britain, played a more significant role in causing the war than has been traditionally suggested.