The German strategy, planned by Alfred von Schlieffen, called for an attack on the weak left flank of the French army by a massive German force approaching through Belgium, while maintaining a defensive stance toward Russia, whose army, Schlieffen assumed, would require six weeks to mobilize. By that time, Germany would have captured France and would be ready to meet the forces on the Eastern Front. The Schlieffen plan was weakened from the start when the German commander Helmuth von Moltke detached forces from the all-important German right wing, which was supposed to smash through Belgium, in order to reinforce the left wing in Alsace-Lorraine. Nevertheless, the Germans quickly occupied most of Belgium and advanced on Paris.
In Sept., 1914, the first battle of the Marne (see Marne, battle of the) took place. For reasons still disputed, a general German retreat was ordered after the battle, and the Germans entrenched themselves behind the Aisne River. The Germans then advanced toward the Channel ports but were stopped in the first battle of Ypres (see Ypres, battles of); grueling trench warfare ensued along the entire Western Front. Over the next three years the battle line remained virtually stationary. It ran, approximately, from Ostend past Armentières, Douai, Saint-Quentin, Reims, Verdun, and Saint-Mihiel to Lunéville.
Meanwhile, on the Eastern Front, the Russians invaded East Prussia but were decisively defeated (Aug.–Sept., 1914) by the Germans under generals Hindenburg, Ludendorff, and Mackensen at Tannenberg and the Masurian Lakes (see under Masuria). The Germans advanced on Warsaw, but farther south a Russian offensive drove back the Austrians. However, by the autumn of 1915 combined Austro-German efforts had driven the Russians out of most of Poland and were holding a line extending from Riga to Chernovtsy (Chernivtsi). The Russians counterattacked in 1916 in a powerful drive directed by General Brusilov, but by the year's end the offensive had collapsed, after costing Russia many thousands of lives. Soon afterward the Russian Revolution eliminated Russia as an effective participant in the war. Although the Austro-Hungarians were unsuccessful in their attacks on Serbia and Montenegro in the first year of the war, these two countries were overrun in 1915 by the Bulgarians (who had joined the Central Powers in Oct., 1915) and by Austro-German forces.
Another blow to the Allied cause was the failure in 1915 of the Gallipoli campaign, an attempt to force Turkey out of the war and to open a supply route to S Russia. The Allies, however, won a diplomatic battle when Italy, after renouncing its partnership in the Triple Alliance and after being promised vast territorial gains, entered the war on the Allied side in May, 1915. Fighting between Austria and Italy along the Isonzo River was inconclusive until late 1917, when the rout of the Italians at Caporetto made Italy a liability rather than an asset to the Allies.
Except for the conquest of most of Germany's overseas colonies by the British and Japanese, the year 1916 opened with a dark outlook for the Allies. The stalemate on the Western Front had not been affected in 1915 by the second battle of Ypres, in which the Germans used poison gas for the first time on the Western Front, nor by the French offensive in Artois—in which a slight advance of the French under Henri Pétain was paid for with heavy losses—nor by the offensive of Marshal Joffre in Champagne, nor by the British advance toward Lens and Loos.
In Feb., 1916, the Germans tried to break the deadlock by mounting a massive assault on Verdun (see Verdun, battle of). The French, rallying with the cry, "They shall not pass!" held fast despite enormous losses, and in July the British and French took the offensive along the Somme River where tanks were used for the first time by the British. By November they had gained a few thousand yards and lost thousands of men. By December, a French counteroffensive at Verdun had restored the approximate positions of Jan., 1916.
Despite signs of exhaustion on both sides, the war went on, drawing ever more nations into the maelstrom. Portugal and Romania joined the Allies in 1916; Greece, involved in the war by the Allied Salonica campaigns on its soil, declared war on the Central Powers in 1917.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.