WWI
Trenches
During trench warfare, opposing armies conduct battle, at relatively close range, from a series of ditches dug into the ground. Trench warfare becomes necessary when two armies face a stalemate, with neither side able to advance and overtake the other. Although trench warfare has been employed since ancient times, it was used on an unprecedented scale on the Western Front during World War I.
It was first used in the civil war but also brought into wwI.The first time it was used in wwI was during the First Battle of the Marne in September 1914, however, the Germans were pushed back by Allied forces. They subsequently "dug in" to avoid losing any more ground. Unable to break through this line of defense, the Allies also began to dig protective trenches.