Napoleon overestimated his ability to handle logistics for distant campaigns. Given how well sacking Moscow turned out, I'm ever so dubious about his ability to march on southern India.
Modern armies need logistic trains. You can't just scavenge it. That works for a 13th century horde, not a 19th century nation.
Sherman would beg to differ. The need for massive logistics support is a modern phenomena that arose from technological development:
1. Jacketed bullets. When you can cast round shot in a sand crucible, bullets are easy to recycle. When they require a machine press, they need to be dragged along behind you.
2. Specialized artillery. Early cannon were mostly just long metal tubes, modern breach loading artillery were far more complicated beasts that required inordinately more tools and spare parts. Additionally once you start losing interchangeability of propellant your logistical burden goes up again.
3. Massive increases in rates of fire. Napoleonic soldiers might carry 80 rounds per soldier. That was still only enough for maybe 30 minutes of sustained fire in the era, but with even the slowest bolt actions you will burn through that in a third of the time.
4. Communications. Napoleon mastered the semaphore and the "march separately, fight together" doctrine, but with the telegraph and later radio, battles became affairs measured in days or weeks. With these longer battles you starting need more and more men, munitions, and spares.
And lastly the mother of all logistical problems:
Fuel.
When you have an army on foot, you just need food. Assuming there are peasants nearby, well they can be robbed a few times. Pretty much literally anywhere worth fighting over there was food for at least the first pass by. If you have horses, then you need fodder or a lot of grass & time to feed them (this is part of the reason no army of the era ever carried food for more than a fraction of the campaign at any given time). Once you get to railroads you are looking at having to move masses of coal (though lumber can work in a pinch) and with internal combustion engines - petroleum products. Logistics simply weren't that bad in the EU era.
You had food - couldn't carry enough to ever feed your army so the availability of food determined war goals (literally the Sun King had to go siege his 3rd priority target because the first two had been picked clean the proceeding campaign seasons). Lead - very easy to recast and well you could often rob the peasants or the churches. Gunpowder - most of the time you bought it from the land you were crossing (e.g. when the French invaded the Netherlands they bought all their gunpowder from Amsterdam), but this and artillery were actually in the supply train (and yes that often meant getting forage for the horses). That's it. Eventually you'd need footwear, but you could often get by without proper shoes or boots (hence why the Russians maintain to this day some idiotic footwear that doesn't require cobblers in use). Eventually you'd need shirts and pants, but again robbing peasants solves so many logistical issues. Paying the army, well again there are peasants to loot (as you know many if not most of the soldiers in the EU era weren't formally paid).
Lastly, before we get all gung-ho about realistic logistics, let's just remember how terrible overland transport (e.g. for cannons) actually was. Britain had an easier time supplying artillery to New Orleans and India direct from London than it did getting cannons to anything in the interior of Spain or France. France, for that matter, could more easily supply forces in Italy than in Navarre. Basically as long as you didn't have something like the Royal Navy interdicting you, you could just about anywhere in the world along the coast easier than you could go 50 miles inland. I mean there is a reason why Gustavus Adolphus serpentined all across central Germany following the rivers; moving his artillery overland would have been a death sentence. When a general completely surrenders strategic initiative, you might realize that realistic logistics would not make invading China harder, China would be about the same ... invading France would get a lot harder.
