Although the
Congress of Erfurt had sought to preserve the Russo-French alliance, by 1811 tensions were again increasing between the two nations. Although Alexander and Napoleon had a friendly personal relationship since their first meeting in 1807, Alexander had been under strong pressure from the Russian aristocracy to break off the alliance with France. In order to keep other countries from revolting against France, Napoleon decided to make an example of Russia.
The first sign that the alliance was deteriorating was the easing of the application of the
Continental System in Russia, angering Napoleon. By 1812, advisors to Alexander suggested the possibility of an invasion of the French Empire and the recapture of Poland.
Russia deployed large numbers of troops to the Polish borders, eventually placing more than 300,000 of its total army strength of 410,000 there. After receiving initial reports of Russia's war preparations, Napoleon began expanding his
Grande Armée to more than 450,000-600,000 men (in addition to more than 300,000 men already deployed in Iberia). Napoleon ignored repeated advice against an invasion of the vast Russian heartland, and prepared for an offensive campaign.
On
22 June 1812, Napoleon's invasion of Russia commenced. In an attempt to gain increased support from Polish nationalists and patriots, Napoleon termed the war the "Second Polish War" (the first Polish war being the liberation of Poland from Russia, Prussia and Austria). Polish patriots wanted the Russian part of partitioned Poland to be incorporated into the
Grand Duchy of Warsaw and a new Kingdom of Poland created, although this was rejected by Napoleon, who feared it would bring Prussia and Austria into the war against France. Napoleon also rejected requests to free the Russian
serfs, fearing this might provoke a conservative reaction in his rear.
The Russians under
Mikhail Bogdanovich Barclay de Tolly avoided a decisive engagement which Napoleon longed for, preferring to retreat ever deeper into the heart of Russia. A brief attempt at resistance was offered at
Smolensk (16–17 August), but the Russians were defeated in a series of battles in the area and Napoleon resumed the advance. The Russians then repeatedly avoided battle with the
Grande Armée, although in a few cases only because Napoleon uncharacteristically hesitated to attack when the opportunity arose. Thanks to the Russian army's
scorched earth tactics, the Grande Armée had more and more trouble foraging food for its men and horses. Along with hunger, the French also suffered from the harsh Russian winter.
Barclay was criticized for his tentative strategy of continual retreat and was replaced by
Kutuzov. However, Kutuzov continued Barclay's strategy. Kutuzov eventually offered battle outside
Moscow on
7 September. Losses were nearly even for both armies, with slightly more casualties on the Russian side, after what may have been the bloodiest day of battle in history: the
Battle of Borodino (see article for comparisons to the first day of the
Battle of the Somme). Although Napoleon was far from defeated, the Russian army had accepted, and withstood, the major battle the French hoped would be decisive. After the battle, the Russian army withdrew and retreated past Moscow.
Napoleon then entered Moscow, assuming that the fall of Moscow would end the war and that Alexander I would negotiate peace. However, on orders of the city's military governor and commander-in-chief,
Fyodor Rostopchin, rather than capitulating, Moscow was
ordered burned. Within the month, fearing loss of control back in France, Napoleon left Moscow.
The French suffered greatly in the course of a ruinous retreat; the Army had begun as over 650,000 frontline troops, but in the end fewer than 40,000 crossed the
Berezina River (November 1812) to escape. The strategy employed by Barclay and Kutuzov had worn down the invaders and maintained the Tsar's domination over the Russian people. In total, French losses in the campaign were 570,000 against about 400,000 Russian casualties and several hundred thousand civilian deaths.
One American study concluded that the winter only had a major effect once Napoleon was in full retreat:
"However, in regard to the claims of "General Winter," the main body of Napoleon's Grande Armée diminished by half during the first eight weeks of his invasion before the major battle of the campaign. This decrease was partly due to garrisoning supply centres, but disease, desertions, and casualties sustained in various minor actions caused thousands of losses. At Borodino on 7 September 1812 — the only major engagement fought in Russia — Napoleon could muster no more than 135,000 troops, and he lost at least 30,000 of them to gain a narrow and Pyrrhic victory almost deep in hostile territory. The sequels were his uncontested and self-defeating occupation of Moscow and his humiliating retreat, which began on 19 October, before the first severe frosts later that month and the first snow on 5 November."
