Bloody scraps of metals!

Imagine mechanized war just does not work.
Engines fail often and lack spare parts, tyres get bogged down in mud, oil is difficult to be brought to the frontline, specialist mechanics are difficult to train, armoured division are a LOT more costly than infantry ones (and often a molotov cocktail is sufficient to eliminate a tank/panzer), limited arc of vision from inside a tank make them too vulnerable, tank crews often suffer from carbon monoxide intoxycation, fuel is an inflammable substance, etc.
All in all, the idea of mechanized war is a total nonsense.
What are the consequences?
 
At what point does mechanised warfare become untennable? Are railways and horse drawn artillery OK, what about trucks drawing artillery on sealed roads behind the lines?

My guess is that warfare would be mechanised up to the point at which it becomes too hard.
 
Twilight 2000 or Einstein's Fourth World War

What makes mechanized warfare possible are industry and access to resources (labor, capital, raw materials, skills,technology, and energy) to feed it.
A major dieback in population, an EMP strike zapping the Internet and disruption in energy supplies would do nicely to break things down to an almost feudal level, without some heroic attempts to preserve the knowledge and skills of modern society. The scope of the combatants (how big the army and what it has to fight with) are directly related to the resources it can access and develop.
One reason the US Army is so into the quick-war doctrine is that modern weaponry eats ammo, fuel, and spare parts voraciously under combat conditions and it takes six out of ten boots in uniform to keep the gear running, not actually shoot anything or anyone. (I'm including logisitics personnel shuffling supplies and trashed/fixed gear back and forth).
A mass-maneuver shooting war with a mechanized opponent lasting more than twelve weeks would severely tax our capabilities, because we no longer produce with the economies of scale as we did during WWII and have been largely using the same tanks, planes, and ships as we had during the 1980's with a bunch of refitted gear, not producing a lot of new stuff because it's become so @#$% expensive per unit. That's why F-22, F-35/JSF, DDX, Crusader have been shelved.
My point is, gear would start breaking down as the supply train dries up and the repairs become ever-more dodgy improvisations until it can't go anymore or gets wrecked in combat or cannibalized for parts. Then after the Mad Max era, where the survivors scuffle for the scraps of civilization, you'd have folks going back to horses and crossbows. Sound cool?
 
Well, in real life or more or less was all of those things...and yet it still took over. You're going to have to have an extremely high pain threshold before people give up the idea.
 
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