Although trenches were used in ancient and medieval warfare, they are mainly associated with WWI. Because the introduction of rapid-firing artillery made the infantry charges of earlier wars virtually impossible, opposing sides attacked and defended from sets of trenches dug into the ground in zigzag patterns. The advent of mechanized warfare made it possible to circumvent these defenses, however, and trench warfare was little used in WWII. In what more recent wars was it nevertheless employed? Discuss