When the Germans invaded Belgium in August 1914, the Belgian army defended its homeland and then fell back to join a rapidly landed British army corps near the Franco-Belgian border. Instead of quickly capturing Paris in a vast encircling movement, German soldiers were advancing slowly along an enormous front. On September 6 the French attacked the German line at the Battle of the Marne. For three days France threw everything into the attack, forcing the Germans to fall back (Map 28.3).

The two stalled armies now dug in behind rows of trenches, mines, and barbed wire. A “no-man’s land” of one hundred to three hundred yards lay between the two combatants. Eventually an unbroken line of trenches stretched over four hundred miles from the Belgian coast to the Swiss frontier. By November 1914 the slaughter on the western front had begun in earnest. For four years battles followed the same plan: after ceaseless heavy artillery shelling to “soften up” the enemy, young soldiers went “over the top” of the trenches in frontal attacks on the enemy’s line.

The human cost of trench warfare was staggering, while territorial gains were minuscule. In the Battle of the Somme in summer 1916, the British and French gained an insignificant 125 square miles at a cost of 600,000 dead or wounded. The Germans lost 500,000 men. That same year the unsuccessful German campaign against Verdun cost 700,000 lives on both sides. The slaughter was made even greater by new weapons of war — including chemical gases, tanks, airplanes, flamethrowers, and the machine gun.

On the eastern front, the Russians moved into eastern Germany but suffered appalling losses against the Germans at the Battles of Tannenberg and the Masurian Lakes in August and September 1914 (see Map 28.3). German and Austrian forces then reversed the Russian advances of 1914 and forced the Russians to retreat deep into their own territory in the 1915 eastern campaign. A staggering 2.5 million Russians were killed, wounded, or taken prisoner.

These changing tides of victory and hopes of territorial gains brought neutral countries into the war. In May 1915 Italy joined the Triple Entente of Great Britain, France, and Russia in return for promises of Austrian territory. In September Bulgaria joined the Triple Alliance in order to settle old scores with Serbia.