A single assassination triggered war only because the underlying system was already primed to explode

Meyer opens with the assassination of Archduke Franz Ferdinand in Sarajevo by a Serbian nationalist in June 1914, but he's careful to frame the killing as a spark rather than the true cause of the war that followed. The deeper explanation lies in a tangle of alliance obligations, imperial rivalries, and military mobilization plans that had been building for decades among the Austro-Hungarian, German, Russian, French, and British governments, any one of which could plausibly have avoided catastrophe with different choices in the following weeks.

He traces how Austria-Hungary's demand for punitive concessions from Serbia, backed by German assurances of support, set off a chain reaction: Russian mobilization in support of Serbia, German mobilization against Russia, and French involvement through treaty obligations, each step justified by leaders who believed they had no real alternative. Meyer's point is that the July crisis reveals a system so brittle that almost any serious provocation would have produced a similar cascade.

Takeaway: the war's real cause wasn't one bullet, it was a continent-wide system with no working brakes.