Trench warfare
Trench warfare occurred when a revolution in firepower was not matched by similar advances in mobility, resulting in a grueling form of warfare in which the defender held the advantage. On the Western Front in 1914–1918, both sides constructed elaborate trench, underground, and dugout systems opposing each other along a front, protected from assault by barbed wire, mines, camouflaged trapping pits, and other obstacles. The area between opposing trench lines (known as "no man's land") was fully exposed to artillery fire from both sides. Attacks, even if successful, often sustained severe casualties.
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.