> For example, his advice to live off the enemy's supplies instead of bringing your own (which would be very expensive and cause economic problems that he surprisingly addresses). This is good advice in many cases, and has been done throughout history, but it can also go very wrong. Consider Napoleon's invasion of Russia where Russia just burned down everything in the path of the French army in order to deny them supplies
It's not "good advice in many cases", it was (prior to the availability of first railroads and then trucks, and with the very notable exception of all-cavalry armies operating on grass steppe) an extremely basic fact on how an army works. Bringing your own supplies was, over long distances, not just bad advice, nor just hard to do, it was logistically impossible. Napoleon did not (yet) have the choice to do it any other way, the alternative was not to invade Russia, or to do it piecemeal while consolidating and developing conquered parts before moving on, which would have taken decades.
This is not true at all. Supply lines have existed as long as organised armies have existed. Many major military campaigns have made use of supply depots, supply ports, supply trains (on pulled wagons, long before what we now call trains existed), etc. Napoleon also made use of them. Only, it's very expensive, and it's a lot cheaper to live off the land. Only living off the land also takes time, so if you want to move fast, arranging your supplies up front allows your army to move faster. But long supply lines deep into enemy territory are incredibly expensive, as well as vulnerable to raids. Which means you need to protect them, which makes them even more expensive.
It was not logistically impossible, it was incredibly expensive. And more so the deeper into enemy territory you get. But plenty of armies throughout history did bring their own supplies.
> Rather than reinvent the wheel here, I’ll note that K. Chase (op. cit.) ran these numbers assuming two-horse 1400lb wagons and found that assuming the army acquired no local food (but could get grass for the horses), for a group of thirty infantryman the first wagon doubles their range from 120 to 240 miles (less really, horses cannot be worked so many days consecutively). Doubling again to around 400 (accounting for horse rest time) requires not two but six wagons for thirty men. To double the range again would require more wagons than men.
By around 3 months of campaign, you need more wagons than men to provide a supply train that doesn't require local forage for your army (but require it for your animals). Supply trains in pre-modern times are less "let's provide all the food for our army on campaign" and more "provide the mobile granary to store everything we're looting for a few days before it's eaten." In premodern times, absent the possibility of naval supply, not foraging the local land for your food is logistically impossible.
I never said it's a good idea for all situations, but for some. It was most definitely done, so the claim that it was impossible is clearly nonsense. It was impossible in some circumstances, but possible in others. And of course it's a good idea to use local resources when they're available, but there's a big difference between that and relying entirely on local resources.
Armies used supply lines over land during the 100 Years War[0], Romans maintained a network of supply depots[1]. It happened during most time periods.
Just like there's a limit to how much food you can move how far, there's also a limit to how large an army can live off the land. Beyond a certain size, you simply need to bring your own supplies. In fact, one of Napoleon's innovations was that he organised his armies in a way that allowed larger armies than before to live off the land. But larger armies did exist before; they just had to bring supplies.
And of course you're not going to supply a large army over a distance of hundreds of miles using just carts. They used ships where possible, they used supply depots, and organised the most efficient routes by which to maintain those. But you bet lots of land travel was involved as well.
It's absolutely true, and the only thing I missed and you are not wrong about is that supplying armies via ship was possible, if they only operated near ports. That's exactly why the Roman empire conquered lands around the Mediterranean but never advanced deeply into central Europe or the middle East.
But no, neither depots nor wagon trains can supply a large army over long distances. It's not too expensive, it's impossible, because the animals that draw the wagons (and build the depots) themselves eventually consume more supplies than they can draw.
A force of 2000 men over 100 miles? Yeah, that may be in "doable, but expensive" territory. 50,000 men over 500 miles? Forget it.
They did conquer the entirety of Gaul, which is not just coast. And France isn't small. Romans built roads, supply depots, carried supplies on pack animals.
And if you think you can move 50,000 soldiers 500 miles deep into enemy territory without supply lines, you can forget about that too. Napoleon did use supply lines from Poland into Russia. Remember: we're talking about Sun Tzu's advice not to bring your own food but take it all from the enemy land, and I'm saying that doesn't work in all circumstances. I'm not saying it never works. But there are very good reasons why historically, large armies did rely on supply lines.
The importance of logistics for large armies is widely underestimated.
If you abandon your supply base, and try to live of the (enemy's) land, you have to advance continuously and quickly, like Sherman's successful campaign in Georgia and the Carolinas. If you rest for even a day or so, you deplete the available "forage" (i.e. the resources of the civilian population).
If you stick with your supply base, then a large part of your force has to be devoted to defending the supply lines; and those supply lines have to be manned, and consume supplies themselves. In the time before internal combustion engines, it was hard to maintain supply lines for armies larger than about 80,000 men, because the fodder required for horses began to exceed the supplies needed by the soldiers. Putin ran into logistics problems almost immediately; Russia depends internally on railways very heavily, but his army had to de-train at the border and switch to trucks, on narrow roads, lined with forests.
It's not "good advice in many cases", it was (prior to the availability of first railroads and then trucks, and with the very notable exception of all-cavalry armies operating on grass steppe) an extremely basic fact on how an army works. Bringing your own supplies was, over long distances, not just bad advice, nor just hard to do, it was logistically impossible. Napoleon did not (yet) have the choice to do it any other way, the alternative was not to invade Russia, or to do it piecemeal while consolidating and developing conquered parts before moving on, which would have taken decades.