Schlieffen Plan
Germany's plan to knock France out in six weeks by sweeping through neutral Belgium, which instead pulled Britain into World War I.
The Schlieffen Plan was Germany's answer to its worst strategic nightmare: a war on two fronts, against France in the west and Russia in the east, at the same time. Named for Count Alfred von Schlieffen, chief of the German General Staff from 1891 to 1905, it proposed to solve the problem by refusing to fight both enemies at once. Germany would knock France out fast, in about six weeks, then turn to face the slower-mobilizing Russians. When it broke down in 1914, it helped produce the four-year slaughter of the Western Front.
The concept
Schlieffen set out the idea in a memorandum written in December 1905, on the eve of his retirement. Because France's border with Germany was heavily fortified in Alsace-Lorraine, a frontal assault would bog down. His solution was a giant wheeling movement. The German army would mass overwhelming strength on its right wing, drive northwest through neutral Belgium, sweep around Paris from the west, and trap the French army against its own fortifications. Schlieffen wanted the right wing so strong that, in the phrase attributed to him, the last man on the right could brush the Channel with his sleeve.
The plan was a gamble against the clock. It assumed Russia would take roughly six weeks to mobilize its vast but sluggish army. Germany would use that window to destroy France, then shuttle its forces east by railway to meet the Russians before they could strike deep into German territory. Timetables, not maps, were the heart of it.
Moltke's modifications
Schlieffen's successor, Helmuth von Moltke the Younger, inherited the concept and altered it. Nervous about leaving the German homeland exposed, Moltke strengthened the defensive left wing at the expense of the all-important right, and he spared the Netherlands from invasion to preserve a neutral windpipe for trade. Whether these changes doomed the plan, or whether the plan was never workable to begin with, remains contested.
What is not contested is the diplomatic catastrophe built into it. Marching through Belgium meant violating Belgian neutrality, which Britain, Prussia, and the other great powers had guaranteed in the 1839 Treaty of London. When Germany invaded on August 4, 1914, dismissing the treaty as a 'scrap of paper,' Britain declared war the same day. A plan meant to win a two-front war had helped guarantee a wider one, with the British Empire added to Germany's enemies.
The failure and the myth
In practice the German advance fell short. Exhausted, outrunning its supplies, and with its right wing weakened, the army was halted at the First Battle of the Marne in September 1914. Both sides then dug in, and the war of movement congealed into the trenches that would define the conflict. The dream of a six-week victory became four years of attrition.
Historians have since argued about whether a single fixed 'Schlieffen Plan' ever really existed. From 1999 the military historian Terence Zuber contended that the famous Plan was largely a postwar invention by German officers eager to blame a dead man's rigid blueprint rather than their own decisions. Most scholars reject his strongest claim but concede the point that matters: the 1905 memorandum was a set of ideas, not a binding operational script. Either way, the deeper lesson stands. A war plan that treated the invasion of a neutral country as a mere technical detail helped turn a continental quarrel into a world war.