The great vastness of Russia. The retreating of the Russians instead of fighting a full battle, and the burning and destroying of everything the French could use, especially food, all played their part. As the French advanced there was little food the troops could scavenge, so they began to starve. The final straw was the Russian winter. Most French troops were poorly equipped to withstand the bitter cold. Napoleon thought that invading Russia would be quick and easy! As the French was forced to retreat, with many dying on the slow march home, the Russian forces and Cossacks began picking off stragglers and attacking the column in hit and runs.Incidently, Adolf Hitler and Nazis Germany made the same mistake in World War II. They thought it would be a quick and easy victory; and the German army (or what remained of it) were also forced to retreat out of Russia.Hitler would have been wise to study Napoleon's retreat, but he made the same mistake as Napoleon!