First of all, the leaders of the warring country had more of an attacking style to this war. And they were also super confident in their armies, and they thought that they all would overpower each other. When the war started, everyone underestimated each other’s military strength and were forced to take a defensive stance. This is how trench warfare was born.
Secondly, trenches provided à lot of defense, which made it harder for attackers to mount fronts and assaults. For attackers to mount attacks, they would have to cross