As the German army retreated before achieving its objective during the Battle of Verdun, the French army won. The battle lasted between February and July, resulting in hundreds of thousands of casualties on both sides.
Late in 1915 and early in 1916, Germany decided the only way for it to win the war was on the western front. General Erich von Falkenhayn decided to wage battle at Verdun, which was an ancient pre-Roman fortress. He hypothesized that the French would have to pour significant manpower into the battle, leading to enough casualties for them to lose the war, which would then allow Germany to focus on defeating the British.
The Battle of Verdun began Feb. 21, 1916. Despite having evidence to suggest that the Germans were preparing to attack, the French were unprepared. By the time French reinforcements arrived on Feb. 25, the German army had seized Fort Douaumont. Germany continued to advance through the area until June, making further gains during the month, including Fort Vaux. On July 1, 1916, the allied forces began their offensive on the Somme. As a result, the German army no longer had the resources to commit to both fronts, forcing them to retreat. Around 430,000 men were lost on each side, making it one of WWI's most costly battles.