Trench warfare

Land warfare involving static fortification of lines

Trench warfare is a type of land warfare using occupied lines largely comprising military trenches, in which combatants are well-protected from the enemy's small arms fire and are substantially sheltered from artillery. It became archetypically associated with World War I (1914–1918), when the Race to the Sea rapidly expanded trench use on the Western Front starting in September 1914.

This keyword could refer to multiple things. Here are some suggestions: