The Chain Reaction

The shooting did not start the war on its own. It tripped a web of alliances and ultimatums that dragged the whole continent in within weeks.

• Austria-Hungary handed Serbia an impossible ultimatum
• Serbia's protector, Russia, began to mobilize
• Germany backed Austria and declared war on Russia, then France
• German troops crossed into Belgium, pulling in Britain

In just over a month, most of Europe was fighting. By 1918 the toll was staggering: over 20 million dead, four empires gone, and the bitterness that would feed a second world war — all set off because one driver took a wrong turn in Sarajevo.