So Napoleon goes into Russia with over 600,000 men and leaves with a few thousand. This was caused by multiple factors of course but I'm curious about the preparations made before the invasion and anticipated needs of the army versus the reality experienced while in Russia. Did Napoleon expect to live off the land and was surprised by the Russians burning everything as they retreated, or were his preparations just inadequate regardless of the circumstances?
The French Army was very well prepared for the Russian Campaign as evidenced that Napoleon achieved tactical and strategic victory in slightly over two months. The main problem was that Russian did not make much of this fact and continued to operate as nothing ever happened, much to Napoleon's dismay.
Russian Campaign was envisioned as a relatively short affair, scheduled for few months. The first detachments of the Grandee Armee enter Russian on 23rd June 1812 and on 19th August the French capture Smolensk. A month later, on 14th September, Napoleon enters Moscow. At this moment, French control three important Russian cities (Polotsk was captured in the meantime by II and VI Corps under Laurent Saint-Cyr) and narrow corridors allowing supply, while Russians, who still have large reserves of troops, control basically every other part of the vast Russian territory with more than enough capacity to harass French supply lines stretched over almost 600 miles (in case of Moscow) and conduct the scorched earth tactics to deny the terrain to the enemy a prevent local foraging. As a part of this tactics, inhabitants of Smolensk and Moscow were evacuated with all the supplies they could take and the city was burned to further reduce its usefulness. So, French Grand Army reached the heart of European part of the Russian Empire and became stranded in hostile territory with little chance of improving their situation. This was a deliberate strategy envisioned by tsar Alexander I and General (later Field Marshall) Mikhail Kutuzov while also favoured by generals Pyotr Bagration and Mikhail Barclay de Tolly.
So, to sum it up, Napoleon's Grande Armee was adequately prepared for the operation planned and executed by the Napoleon who based it on all other operations he has overseen so far. It simply wasn't prepared for the completely different strategy adopted by Russians that made the campaign unlike any other. One could also note that Napoleon overestimated his capabilities of territory control, as in comparison with other European countries, Russia was very vast and sparsely populated making control difficult even for almost 700.000-strong army.