trench warfare: Although trenches were used in ancient and medieval warfare, in the American Civil War, and in the Russo-Japanese War (1904–5), they did not become important until World War I. The introduction of rapid-firing small arms and artillery made the infantry charges of earlier wars virtually impossible, and the war became immobile, with the contenders digging thousands of miles of opposing trenches fronted by barbed wire. To break the stalemate various methods and new weapons were tried; tremendous artillery barrages sought to devastate the enemy and blow a gap in his trenches; trench mortars, hand grenades, poison gas, and tanks were used. It nevertheless remained a war of attrition, with artillery duels and infantry attacks behind creeping artillery barrages. The idea of an uninterrupted line defense held the imagination of the French and German general staffs between the two world wars, and they built lines of field fortifications known as the Maginot Line and the Siegfried Line. The advent of mechanized warfare made it possible to circumvent such defenses, and World War II was a war of movement. However, in the last stages of the Korean war both sides established fortified positions across the Korean peninsula, and a stalemated situation similar to that of World War I came into play.
See L. Wolff, In Flanders Fields: the 1917 Campaign (1958).