Who really started World War I: Germany, everyone, or no one?

Historians still disagree, and the honest answer is that it depends on whom you ask. Identifying the causes of World War I remains a debated issue. The war began on 28 July 1914 and ended on 11 November 1918, leaving an estimated 17 million dead and 25 million wounded, and the question of who was responsible has been argued ever since.

The long background is the alliance system. By August 1914 the powers had formed two competing sets: Germany and Austria-Hungary on one side, and Russia, France and Britain on the other. On the Entente side, key markers were the 1894 Franco-Russian Alliance, the 1904 Entente Cordiale with Britain and the 1907 Anglo-Russian Convention. The Entente was not an alliance of mutual defence, so in 1914 Britain felt free to make its own decisions.

The most famous disagreement is between two books. In the early 1960s the German historian Fritz Fischer advanced the thesis that responsibility for the outbreak of the war rested solely on Imperial Germany. By the 1980s, according to the historian Annika Mombauer, a new consensus had emerged: few historians agreed wholly with Fischer's thesis of a premeditated war, but it was generally accepted that Germany's share of responsibility was larger than that of the other great powers.

Then, in The Sleepwalkers, Christopher Clark argued that no sole country was to blame and that each country unwittingly stumbled into war. Clark concluded that while all the continental powers risked a general war, none sought that war. The debate remains open.