Trench warfare
Trench warfare prevailed on the Western Front from late 1914 until the Germans launched their Spring Offensive on 21 March 1918. After the buildup of forces in 1915, the Western Front became a stalemated struggle between equals, to be decided by attrition. Frontal assaults, and their associated casualties, became inevitable because the continuous trench lines had no open flanks. Casualties of the defenders matched those of the attackers, as vast reserves were expended in costly counter-attacks or exposed to the attacker's massed artillery. There were periods in which rigid trench warfare broke down, such as during the Battle of the Somme, but the lines never moved very far. The war would be won by the side that was able to commit the last reserves to the Western Front.
Christmas truce
Truces between British and German units can be dated to early November 1914, around the time opposing armies had begun static trench warfare. At this time, both sides' rations were brought up to the front line after dusk, and soldiers on both sides noted a period of peace while they collected their food. By 1 December, a British soldier could record a friendly visit from a German sergeant one morning "to see how we were getting on". Relations between French and German units were generally more tense, but the same phenomenon began to emerge. In early December, a German surgeon recorded a regular half-hourly truce each evening to recover dead soldiers for burial, during which French and German soldiers exchanged newspapers. This behaviour was often challenged by junior and senior officers; the young Charles de Gaulle wrote on 7 December of the "lamentable" desire of French infantrymen to leave the enemy in peace, while the commander of 10th Army, Victor d'Urbal, wrote of the "unfortunate consequences" when men "become familiar with their neighbours opposite". Other truces could be enforced on both sides by weather conditions, especially when trench lines flooded in low-lying areas, though these often lasted after the weather had cleared. On the Eastern Front, Fritz Kreisler reported incidents of spontaneous truces and fraternisation between the Austro-Hungarians and Russians in the first few weeks of the war.