I learned, in my high school history classes, that World War I was fought in the trenches and that the casualties were huge. Furthermore, the implication (sometimes explication) from my history teachers was always that the casualties were so huge because the soldiers were being led by incompetent men.
Where did the commanders of both sides of World War I (Petain, Falkenhayn, Haig, etc.) screw up? What mistakes did they make in planning their strategies and tactics that cost so many lives? Or was trench warfare inevitable with the technologies of the time?
You can read a nice explanation about it here https://www.reddit.com/r/AskHistorians/comments/1dh3u8/why_did_generals_in_ww1_think_it_was_a_brilliant/c9q8u7n by u/halfmanhalfsquidman
Especially these paragraph:
So in short, no they were not ignorant. Their plans were flawed but were essentially what they had to work with at the time. Eventual improvement in artillery tactics by a pretty smart guy named Colonel Georg Bruchmuller and stormtroop tactics by the infantry allowed the brief breaking of the cycle of earlier battles, but the inability for effective exploitation of these gaps in enemy lines led to a failure to end the war before an exhausted German Army began to fall back to the Hindenburg line and beyond, while the German Empire imploded on the home front.
Also here u/mootmute wrote about the effectiveness of some of the tactics that were employed.