"Actually more casualties were suffered on the advance to Moscow than on the retreat."
This October 19th marks the 205th anniversary of the start of Napoleon's fateful retreat from Moscow. The march lasted nearly two months and cost tens of thousands of lives, with the remnants of Napoleon's army re-crossing the Russian border on December 12th.
Much is made of the destruction of the "Grand Army of 500,000" by the cold weather and the Cossacks, but this is yet another cliche of World history that doesn't accord entirely with all the facts.
The first point to make is that the actual force that started the retreat from Moscow was only around 95,000 men, not the half million that is given as the force invading Russia. This force was then joined by an additional 36,000 men on its march home. These were the remnants of 82,000 men detached previously to guard the Northern flank of the advance. From this "retreating force" of 131,000 men, around 10,000 finally exited Russia on the 12th of December.
Other parts of the Grand Army, fared better. The Austrian and Prussian contingents suffered relatively few casualties; while there were also many deserters and invalids who managed to make it back before the main retreat. In addition to this, there were also around 100,000 prisoners who were later released by the Russians.
Actually more casualties were suffered on the advance to Moscow than on the retreat. Napoleon's main force consisted of 250,000 men. This crossed the Russian border on the 24th of June. By the time they reached Smolensk, 75,000 men had been lost, mainly to disease. On the way to Moscow more died from disease and fighting, including around 30,000 at the Battle of Borodino. Of course, the Russians had suffered badly as well, losing so many men at Smolensk and Borodino that they were unable to fight another major battle against Napoleon's main battle army.
In actual battle Napoleon's main army—made up mainly of French, Poles, and Italians—had the edge on the Russians, and could just about outfight them. Surprisingly the Russians were also willing to give them this chance (I guess no one likes to see their native land desecrated by an invading army).
The 40,000 Russian lives wasted at Borodino could have been better spent attacking Napoleon's extremely long lines of communication, conducting guerrilla operations, or carrying out a scorched earth policy. They were finally forced into this course of operations after their main battle army had been battered and weakened to the point where it couldn't face Napoleon in direct battle.
But what really decided the war in the Russians' favour was Napoleon's own deeply ingrained military habits, formed early on in his first big campaign, his invasion of Italy in 1797.
In that war he clearly followed the "Strategy of the Central Position," taking up a central position that would attract attacks from different directions that he could then pivot towards and defeat in detail. This tendency was probably based on his study of the campaigns of Frederick the Great, who fought off converging French, Russian, and Austrian armies by moving his forces from one front to another along his shorter internal lines of communication.
This "Strategy of the Central Position" became a feature of Napoleon's subsequent campaigns—usually featuring a strong push into the heartland of the enemy to attract converging attacks that he could then beat off in detail. His invasion of Russia was an attempt to do this on a massive scale. But his big mistakes were to underestimate the vastness of Russia and to overestimate its "centrality." Even Moscow, its ancient capital and spiritual centre, lacked the requisite centrality.
This is due to topography. Take a look at a map of Europe and you will see that it is tight and narrow in the West and vast, sprawling, and shapeless in the East. Western European areas, like Flanders, Northern Italy, the Upper Danube Valley, etc., form perfectly sized crucibles for the type of strategy that Napoleon favoured. These are also areas that have many assets in terms of valuable towns and cities that can be seized to provide loot, and also to provoke a definite enemy response. Once you intrude yourself in this way, the enemy will basically come to you, giving you many advantages.
Russia by contrast is too vast an area to provide similar crucibles. Also, its towns in the 19th century were too insignificant or too far apart to offer the same advantages as those in Western Europe.
As St. Petersburg was the capital, one might wonder why Napoleon moved against the less important city of Moscow. The truth is Napoleon was less interested in taking either city. Instead he wanted to intrude himself into a position that would provoke the Russians to launch converging attacks against him that he could then turn on and overwhelm in detail. He believed the campaign would be over in a few weeks.
The vastness of his army however, forced the main Russian forces to stay united and retreat together, instead of attempting to launch converging attacks from different directions. Overawing the Russians in this way with an overlarge army was another key mistake.
The result of this is that the Russian forces were rolled back further than they wished to be, stopping to put up simplistic linear defence that Napoleon was then able to overwhelm at Smolensk and Borodino, but unable to crush, leading to the renewal of the cycle. The end result of this was that the Franco-Italo-Polish army was sucked ever deeper into Russia in quest of an illusory "central position" that did not exist.
Smolensk was not it, nor even Moscow. When the Russians burnt most of the city following the French occupation, even Napoleon realized this was not the "centre" on which he could base his grand "Strategy of the Central Position."
After staying just over a month in Moscow, it was now clear to him that he had gone too far and wasted the season. An awkward retreat was now his only option; while the only option for his opponent, weakened by the meatgrinder Battle of Borodino, was the kind of harassing guerrilla war that would fortuitously give then the optimum results against an overextended, underinsulated, and retreating enemy.
Source: Empire and Revolution