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.
Battle
Until the 19th century the majority of battles were of short duration, many lasting a part of a day. (The Battle of Preston (1648), the Battle of Nations (1813) and the Battle of Gettysburg (1863) were exceptional in lasting three days.) This was mainly due to the difficulty of supplying armies in the field, or conducting night operations. The means of prolonging a battle was typically by employment of siege warfare. Improvements in transportation and the sudden evolving of trench warfare, with its siege-like nature during World War I in the 20th century, lengthened the duration of battles to days and weeks. This created the requirement for unit rotation to prevent combat fatigue, with troops preferably not remaining in a combat area of operations for more than a month. Trench warfare had become largely obsolete in conflicts between advanced armies by the start of the Second World War.