Final answer:
Trenches became more structured during World War I due to the dominance of defensive strategies and the development of new war technologies.
Step-by-step explanation:
Trenches became more structured during World War I due to the tactical problem created by new technologies of war. The defensive strategy became superior to the offensive strategy, as trenches, machine guns, mines, and modern rifles made it more effective to defend a position rather than charge and try to take the enemy's position. This resulted in a stalemate with both sides constructing their own lines of defensive fortifications, creating a vast network of frontline trenches that stretched for hundreds of miles.