Napoleon crossed the Neman River in Poland with 422,000 men. By the time he got to Moscow, his Grande Armée had been reduced to 100,000 from constant battle and attrition. The Russians practiced slash and burn, leaving nothing for Napoleon's forces to subsist on. The French army retreated.
(media.greatawakening.win)
Winning War History: Russia
Napoleon captured Moscow, and held it for several months. He expected the Russians to surrender, but they didn't. When winter approached, the French army needed to leave Moscow due to lack of food, and supplies. It was not really a "retreat," as the unbeaten army had captured its goal, Moscow., and only left their position to find food and supplies.
Thus demonstrating the need to establish supply routes when advancing. They tought they'd be fine once in the city, but there was nothing. Yes, soldiers need food and ammo, and hospital tents and uniforms and.....So it turned into a rout.