On June 28, 1914, a tubercular Bosnian Serb teenager named Gavrilo Princip shot the heir to the Austro-Hungarian throne in Sarajevo. Within six weeks, every major European power was at war. No one had wanted that war. Every government in 1914 expected a short, sharp conflict, a few brisk battles, peace by Christmas. They got four years of industrial slaughter that killed about ten million soldiers and finished four empires.
The war's causes are still argued about, but the consensus shape is something like: a continent overloaded with dynamite and short on circuit-breakers. Two rigid alliance systems (Triple Entente, Triple Alliance) meant any bilateral quarrel could escalate to continental war. Mobilization timetables — drafted by general staffs in peacetime — were so dependent on railway schedules that, once started, they could not be stopped without losing the war you had not yet begun. A century of nationalism had taught populations to want a heroic conflict. A naval arms race between Britain and Germany had produced mutual suspicion. And the diplomats of July 1914, faced with a crisis they thought they could manage, each took one defensive step after another until none of them controlled the outcome. The war is the canonical example of a structural trap: rational individual decisions producing collective catastrophe.
Every contemporary discussion of escalation dynamics — between the US and China, between Russia and NATO, between India and Pakistan — runs through August 1914 as the case study of how an avoidable war becomes unavoidable, one defensible step at a time.