'trench warfare' definitions:

noun

A struggle (usually prolonged) between competing entities in which neither side is able to win; "the hope that his superior campaigning skills would make a difference evaporated in the realization that electioneering had become a form of trench warfare"

noun

A type of armed combat in which the opposing troops fight from trenches that face each other; "instead of the war ending quickly, it became bogged down in trench warfare"