Germany's master plan for a two-front war required defeating France in six weeks before Russia could mobilize. It almost worked — and its failure condemned millions to four years of trench warfare.
After the Franco-Prussian War, Germany's strategists faced a nightmare: in any future conflict, they would likely fight France and Russia simultaneously. Field Marshal Alfred von Schlieffen, Chief of the German General Staff, spent years working on a solution. His answer was audacity — knock out France first with a massive flanking sweep through Belgium, then turn east to deal with Russia.
The plan required violating Belgian neutrality, which Britain had guaranteed since 1839. German planners accepted this risk, calculating that Britain's response would come too late to matter. When Germany invaded Belgium on August 4, 1914, Britain declared war within hours. The calculation was catastrophically wrong.
The German right wing swept through Belgium and northeastern France, advancing so fast that supply lines couldn't keep up. Soldiers marched up to 25 miles a day in the August heat. By early September, the German 1st Army was within 30 miles of Paris — close enough that Parisians could hear the guns.
Then the plan unraveled. A 50-kilometer gap opened between two German armies near the Marne River. The French, using Paris's railway network to shift troops rapidly, counterattacked into the gap. The Germans were forced to retreat. The 'six-week victory' became a four-year stalemate.
Historians have debated ever since whether the plan could ever have worked. The logistical challenges were immense — 1.5 million men advancing hundreds of miles on foot required supply chains that 1914 technology couldn't support. Martin van Creveld concluded that even a hypothetical victory at the Marne could not have been exploited. The plan may have been impossible from the start.
The deeper irony is that the 'Schlieffen Plan' as popularly understood — a single brilliant blueprint — largely didn't exist. Post-war German generals mythologized it to excuse their failures. Schlieffen had actually written multiple plans for multiple scenarios. The rigid master plan that 'failed' was partly a retrospective invention.