[Suhiir]

It's not just armor it's overall.

The ability to move, communicate, detect and hit opponents has been improving steadily since the advent of the railroad, telegraph, rifled barrel, and the observation balloon.

The Tactics of Napoleon were suicidal in the American Civil War, those of the Civil War suicidal in WW I, etc. etc. While the methods of the last war often work fine vs less technologically sophisticated opponents they're not viable vs top tier ones.

Along with this has come a steady downward spiral in the size of the "key" tactical unit. From the divisions of Napoleon to the brigades of WW I, to the regiments of WW II, to the battalions of Vietnam, to the companies of recent conflicts, to almost the platoon level.