The 500,000 strong Napoleon's army moves through Russia and causes much destruction culminating in the battle of Borodino. The Russian army has to retreat. Moscow is occupied, looted and burned down, but soon Napoleon loses control and has to flee. Both sides suffer tremendous losses in the war, and Russian society is left irrevocably changed.
As Moscow is set ablaze by the retreating Russians, the Rostovs flee their estate, taking wounded soldiers with them, and unbeknownst to them, also Andrei. Pierre, dressed as a peasant, tries to assassinate Napoleon but is taken prisoner. As the French are forced to retreat, he is marched for months with the Grande Armée, until being freed by a raiding party. The French are defeated by Kutuzov in the Battle of Krasnoi. Andrei is recognized and is brought to his estate. He forgives Natasha on his deathbed. She reunites with Pierre and they marry as Moscow is being rebuilt.