After the crushing defeat which its forces had inflicted on France in 1870, Berlin had every reason to expect that France would sooner or later attempt to regain her traditional hegemony on the Continent. In itself, this prospect posed no fatal threat, since the war potential of France at the end of the nineteenth century was only one-half of Germany’s. But the matter looked differently if France had on her side Russia, which by virtue of her geographic location and large standing army was ideally suited to counterbalance German might. Immediately after the conclusion of the Franco-Prussian War, when Russia and Germany were still on friendly terms, Helmuth von Moltke, the German chief of staff, warned his government of the prospect of a two-front war.4 This danger became near-certainty in 1894, when France and Russia signed an accord of mutual defense committing them to come to each other’s aid if attacked by Germany or one of her allies. After 1894, the General Staffs of Germany, France, and Russia concentrated on devising strategies that would turn the prospect of a two-front war to their best advantage.
Germany faced the more serious problem by far, since a general continental war would compel her to fight simultaneously in the west and east. To win such a contest Germany had to desynchronize, as it were, the expected enemy offensives and dispose of them one at a time. Should France and Russia (and, after 1907, England) succeed in coordinating their strategies, Germany faced a bleak prospect, for even her superb army could not cope with the combined forces of the other two great land armies and the world’s leading naval power. This consideration lay behind the Schlieffen Plan, on which the German military set to work in 1895 and which it kept on perfecting down to the smallest detail until the outbreak of World War I. The Schlieffen Plan required that Germany crush France before Russia fully mobilized, and then rapidly shift the bulk of her armies to the east. Its essential feature, its very precondition, was speed: speed of mobilization, speed of offensive operations, and speed of troop transfers. The plan posited a slow pace of Russian mobilization, expected to require 105–110 days, compared with the 15 days estimated for the mobilization of German and Austrian armies.5 This disparity—on paper, as much as three months—offered the opportunity to defeat the French before the Russians were able to come to their assistance.
The Schlieffen Plan provided for up to nine-tenths of the German effectives being allocated to the Western Front. Outflanking the short, heavily fortified, and topographically difficult Franco-German border, the right wing was to execute a wheeling movement across Belgium, encircle and capture Paris, and trap the main French forces. While this decisive campaign was in progress, the Russians were to be held at bay by the main mass of the Austro-Hungarians, reinforced with one-eighth or one-ninth of the German army, deployed along the northeastern frontier and in East Prussia. The Schlieffen Plan called for the French campaign to be completed within forty days of mobilization, by which time the Russian army would have less than half of its manpower under arms. Mobilization was the critical factor: the instant the Russians began to mobilize, the Germans had to follow suit or risk the collapse of their entire war plan.
The Allied staffs knew, in broad outline, what the Germans had in mind.6 After many false starts, the French General Staff adopted what came to be known as Plan XVII. This provided for a defensive posture against the anticipated German thrust through Belgium accompanied by a vigorous assault on the linchpin of the German wheeling operation in the center. This attack was to penetrate German territory and, by threatening to cut off the enemy’s right wing, bring the German offensive to a halt.
The success of Plan XVII depended on Russian assistance. It posited that the Russians would threaten Berlin as soon as the German mobilization was completed—that is, by the fifteenth day of the war. The Russian assault was to compel the Germans to withdraw troops from the Western Front before the issue there had been decided and bring about Germany’s collapse.
