The General Staff had calculated that the French army had to be defeated within six weeks if sufficient forces were to be transferred to meet and defeat the expected Russian attack in the east. That could be done only by the great outflanking movement through Belgium visualized by Schlieffen—a manœuvre aimed not only at defeating the French armies but at surrounding and annihilating them in a Schlacht ohne Morgen—‘a battle without a tomorrow’. Schlieffen’s successor, Helmuth von Moltke, nephew of the great field marshal who had led Prussian forces to victory in 1866 and 1870, modified the plan so as to provide better protection against a possible French invasion of south Germany and to avoid having to invade Holland as well; for, if the war did drag on, a neutral Holland would be essential for the German economy.
After the war Moltke was accused of having ruined Schlieffen’s concept, but later research has shown Schlieffen’s recommendations to have been logistically impossible. A German invasion of Belgium had been generally expected—the railheads constructed along the Belgian frontier gave the game away—but French and British staff calculations had concluded that constraints both of logistics and of manpower would confine the movement to the right bank of the Meuse. It was only the two additional army corps provided by the German military reforms of 1911–12, and the unorthodox use of reservist units as front-line troops, that enabled Moltke to flesh out Schlieffen’s ideas, and mount an attack on a scale that took the Allies completely by surprise.
The Belgians had prepared for a German invasion by constructing a major fortification complex at Liège. To deal with this the Germans employed their major ‘secret weapon’— mobile siege artillery, especially heavy howitzers from the Austrian Skoda works, whose shells crashed through steel and concrete and battered the garrison into surrender. By 17 August they had cleared the way, and the German march through Belgium began.
Before them the German armies drove a flood of refugees who clogged the roads with carts bearing all that they could rescue of their possessions—the first trickle of that immense and miserable flood of uprooted humanity that was to characterize warfare for the rest of the century. Those who remained were treated by the invaders with a harshness intended to pre-empt the kind of ‘people’s war’ of sabotage and assassination that the French had begun to wage against their invaders in 1870. Seeing saboteurs and francs-tireurs even when they did not exist, German troops took and shot an estimated 5,000 Belgian civilians and indiscriminately set fire to buildings, including those of the medieval university of Louvain.
Wildly exaggerated reports of their atrocities were spread in Britain, confirming public support for a war that rapidly came to be seen as a crusade against barbaric German militarism—a view that spread to influential quarters in the United States. If the invasion itself had not been enough to provoke Britain to intervene, the manner in which the German forces enforced their occupation would have created almost irresistible pressure to do so.