After 1870, having defeated France's greatest armies, General Helmuth von Moltke (the elder), Chief of the German High Command, began to make plans for a two-front war against France and Russia. The basis for the plan would be to defend against one power while crushing the other. By the end of the century, France began to rise up as the most formidable adversary. France would not take long to mobilize, and once she did, her armies would launch an immediate attack against Germany. Moltke most certainly took into consideration the fact that Germany still possessed the spoils of the Franco-Prussian War, Alsace and Lorraine, and France would fight vigorously for the return of the lost provinces to the fold.
Moltke's successor, Count Alfred von Schlieffen, resolved to cover the Russian mobilization on the Eastern Front with a single army, and to attack, and annihilate, France. This victory must be swift and decisive, because the Russians would not take long to attack. France must be quickly snuffed out so Germany's armies could be sent East to meet the Russian threat. Very simple idea, but difficult to execute.
The French border at the time was heavily fortified, from the Swiss to the Belgian border. After losing Alsace and Lorraine, the French army, under the guidance of one of Europe's eminent military engineers, General Sere de Rivieres, built a strong fortress line - a battlefield prepared in advance. It consisted of the solidly fortified entranched camps of Verdun, Toul, Epinal, and Belfort. A veritable curtain wall of detached Forts d'Arret and Ouvrages were built along the heights of the Meuse and Moselle between the fortress cities. A gap was intentionally left in the area of Charmes, between Toul and Epinal, to funnel German troops into its bottleneck trap.
How then would a German army of 2 million men attack a French army of the same size, through heavily fortified defenses over prepared terrain? To move South through Switzerland would bring Germany face-to-face with a highly trained, highly patriotic, 500,000 strong Swiss army. Then, after enormous casualties, even if victorious over the Swiss, the Germans would face the same fortified obstacles at Besancon, Langres, and Dijon. The only solution in the North would be for Germany to cut a narrow pathway through the Ardennes between Verdun and Montmedy. Again a disaster waiting to happen.
Thus, only one solution presented itself - to attack through the Condroz gap between the Dutch border, north of Liege, and the Ardennes where there was sufficient space and enough roads and railways to squeeze north of Longwy onto the Belgian plains. By taking advantage of the Belgian railway system, Germany's troops would be quickly transported into Western Belgium and down the Meuse River into France to smash the French Fifth Army before it had time to fully mobilize - Paris, and total victory, were only a few days march from there.
Schlieffen's successor, the elder Moltke's nephew, also Helmuth von Moltke, insisted on exact timetables and manpower strengths for his grand enveloping sweep around the left flank of the French Army. German troops must pour into France before the British arrived, and before the Northern Armies of France had time to fully mobilize. He envisioned a flanking maneuver by the 1st and 2nd Armies on the right wing, the greatest strength of the German army. They would pivot on Metz, and sweep rapidly through Belgium, using her four railway lines, while a smaller force held the German fortress line in Alsace and Lorraine against the anticipated French offensive, Plan XVII. Schlieffen's right wing would sweep across Belgium towards the channel coast then turn south, sweep west of Paris, envelop the allied forces and finally crush them in a double envelopment. She could then turn on Russia.
There were only two problems with the plan - the violation of Belgian neutrality which Germany was obligated to protect, and the city of Liege, which barred the door.
NEXT PAGE--The Fortified Position of Liège(PFL)