Long-simmering rivalries in Europe boiled over into world war when the archduke of Austria, Franz Ferdinand, was assassinated on June 28, 1914. This was the first of a series of events that would lead to what became known as the Central Powers (Austria-Hungary, Germany, Bulgaria, and the Ottoman Empire) fighting against the Allied powers of Great Britain, France, Russia, and eventually Italy, Japan, and Belgium. By November 11, 1918, when an armistice was signed in a railroad carriage at Compiegne, more than 65 million people had died in battle and from man-made famine.

While historians debate the causes of this terrible conflict, most agree that there were some deep underlying trends. Many historians seek to identify specific factors that drove the world toward war, while others focus on the larger power dynamics in play.

For example, some scholars argue that diplomatic failures, like the missed opportunity to slow down military mobilization after the assassination, played a major role. They believe that better diplomacy might have prevented the outbreak of war in Europe.

But other historians find this explanation lacking. They point to deeper forces, like nationalism, that fueled the war. They assert that the assassination simply gave leaders an excuse to use the conflict to deal with pre-existing concerns. They also claim that the large armies of each country—and especially the huge number of young men who enlisted to fight them—made it virtually impossible for statesmen to stop the momentum toward war.