Answer:
Trench warfare is warfare in which opposing armed forces attack, counterattack, and defend from relatively permanent systems of trenches dug into the ground. It is resorted to when superior firepower of the defense compels the opposing forces to "dig in" so extensively as to sacrifice their mobility in order to gain protection. The tactical ancestor of modern trench warfare was the system of progressively extended trenches developed by the French military engineer Sébastien Le Prestre de Vauban in the 17th century. Trenches remained merely a part of siegecraft until the increasing firepower of small arms and cannon compelled both sides to make use of trenches in the American Civil War (1861–65). The trench lines of the Petersburg–Richmond theatre of operations in the final months of that war were the foremost example of trench warfare in the 19th Century.
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