In June of 1812, Napoleon began his fatal Russian campaign. Virtually all of continental Europe was under his control, and the invasion of Russia was an attempt to force Tsar Alexander I to submit once again to the terms of a treaty that Napoleon had imposed upon him four years earlier. Having gathered nearly half a million soldiers, from France as well as all of the vassal states of Europe, Napoleon entered Russia at the head of the largest army ever seen. The Russians, under Marshal Mikhail Kutuzov, could not realistically hope to defeat him in a direct confrontation. Instead, they began a defensive campaign of strategic retreat, devastating the land as they fell back and harassing the flanks of the French. As the summer wore on, Napoleon's massive supply lines were stretched ever thinner, and his force began to decline. By September, without having engaged in a single pitched battle, the French Army had been reduced by more than two thirds from fatigue, hunger, desertion, and raids by Russian forces.

Nonetheless, it was clear that unless the Russians engaged the French Army in a major battle, Moscow would be Napoleon's in a matter of weeks. The Tsar insisted upon an engagement, and on September 7, 1812 with winter closing in and the French army only 70 miles (110 km) from the city of Moscow, the two armies met at Borodino Field. By the end of the day, 108,000 men had died - but neither side had gained a decisive victory. Kutuzov realized that any further defense of the city would be senseless, and he withdrew his forces, prompting the citizens of Moscow to began a massive and panicked exodus. When Napoleon's army arrived on September 14, they found a city depopulated and bereft of supplies, a meagre comfort in the face of the oncoming winter. To make matters much, much worse, fires broke out in the city that night, and soon the French were lacking shelter as well.

After waiting in vain for Alexander to offer to negotiate, Napoleon ordered his troops to begin the march home. Because the route south was blocked by Kutuzov's forces (and the French were in no shape for a battle) the retreat retraced the long, devastated route of the invasion. Having waited until mid-October to depart, the exhausted French army soon found itself in the midst of winter-in fact, in the midst of an unusually early and especially cold winter. Temperatures soon dropped well below freezing, cossacks attacked stragglers and isolated units, food was almost non-existent, and the march was five hundred miles. Only ten thousand men survived.

The campaign ensured Napoleon's downfall and Russia's status as a leading power in post-Napoleonic Europe. Yet even as Russia emerged more powerful than ever from the Napoleonic era, its internal tensions began to increase.