Be careful not to compare industrialized warfare to pre-industrial war. They are vastly different. Prior to the railroad, it was almost impossible to keep an army of over 10,000 men supplied for long in any one area. Historically, the size of ancient’s armies has been exaggerated by their contemporaries. The Napoleonic war and especially the US cινιℓ ωαrs were the first time that truly MASSIVE armies could be fielded against each other.
Europeans sent watchers to study the tactics of US generals in the cινιℓ ωαr because armies of such a massive size fighting against each other had never been seen before in the west.
Mass conscription and the railroad truly changed the face of war.