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.
Western Front (World War I)
To break the deadlock of trench warfare on the Western Front, both sides tried new military technology, including poison gas, aircraft and tanks. The adoption of better tactics and the cumulative weakening of the armies in the west led to the return of mobility in 1918. The German Spring Offensive of 1918 was made possible by the Treaty of Brest-Litovsk that ended the war of the Central Powers against Russia and Romania on the Eastern Front. Using short, intense "hurricane" bombardments and infiltration tactics, the German armies moved nearly to the west, the deepest advance by either side since 1914, but the result was indecisive.