Trench warfare is a set of fighting techniques that predominated in the struggle between the Allied and Central Powers during World War I. In its most characteristic form, trench warfare involves two forces digging fortifications and fighting in place, without significant mobility, until superior attrition turns the tide decisively against one faction.
In trench warfare, opposing forces carry out combat operations from fixed positions in battles that can last for months or years. It typically results in cases where defensive fortification is vastly superior to offensive maneuver, and neither side is able to gain a decisive advantage.
Trench warfare was adopted on the Western Front during World War I in September 1914, after the German advance was turned back near the Marne. The resulting stalemate lasted until the major Allied breakthrough four years later. During that period, front-line soldiers lived in a vast network of opposing trenches that were separated by distances shorter than the range of a rifle in some places. In places where the sides were close enough to shoot at each other, sniper fire and artillery were routinely used to inflict casualties.
Frontal assaults are generally ineffective in trench warfare, and the death toll from such tactics in World War I was in the millions.