I haven't studied a lot of battles per se more like the history leading up to and it's after math.But one interesting point i had read that 2 years - 1914 and 1918 suposedly had the most casualties. The years '15-'16-'17 though certainly brutal and miserable were trench warfare with very little agency besides the usual mass charges that proved foolish and deadly then everyone returned to Hunkering down again.Many troops succumbed to the elemnets and all sorts illnesses chronic/disabling sickness dysentery,diarrhea,typhus,typhoid and such.Not forgetting the Spanish Flu that could have started on the battle fields themselves and not in Spain
Point being is when armies were marching they made much easier targets and things ramped up late in the war. Like when doughboys came and they went on more forced marches to flank enemy positions forcing the war to end one way or another