The Congress of Erfurt sought to preserve the Russo-French alliance and the leaders had a friendly personal relationship after their first meeting at Tilsit in 1807. However, on June 23, 1812, Napoleon went to war with Russia. The French invasion of Russia defeated many Russian cities and villages, but by the time they reached Moscow it was winter. Due to the Russian army's scorched earth tactics, the French found little food for themselves and their horses. Napoleon's army was unable to defeat the Russians. The Russians began to attack. Napoleon and his army had to go back to France. The French suffered greatly in during Napoleon's retreat. Most of his soldiers never returned to France. His army was reduced to 70,000 soldiers and 40,000 stragglers, against more than three times as many Allied troops. Finally at the 1813 Battle of the Nations he was defeated by the Allies: Sweden, Russia, Austria, and Prussia.