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.
Trench warfare
A recent example of trench warfare is the War in Donbass. To consolidate and defend their territory, government and rebel forces have dug trenches and have initiated warfare reminiscent of World War I, with troops staying in and fighting from trenches for months at a time using cement mixers and excavators at their lines for digging network tunnels and deep bunkers for protection. Since the Minsk peace agreements the front lines have not moved significantly and the two sides mostly fire mortars and sniper shots at each other. As a result both sides have dug elaborate networks of trenches and deep bunkers for protection.