Napoleon feared his empire would fall after his death. This love of power led to his downfall with three huge mistakes.
Napoleon came up with the Continental System, a blockade to keep the British from trading with other countries. This seemed to work at first. But Great Britain had a stronger navy, and made a better blockade around the French. However, smugglers still got goods in. Also, America got upset, and began the War of 1812 with Britain. This weakened them, but did not destroy them.
CONTINENTAL SYSTEM OF 1806
Napoleon tried to get Portugal to accept the Continental System, and when they refused, he invaded Spain. The Spanish were already upset because Napoleon's brother was their ruler. Now, Spanish guerrillas (groups of peasant fighters) beat out Napoleon, and he lost 300,000 men.
THE PENINSULA WAR OF 1808
Napoleon thought it would be a good idea to invade Russia in the winter. The Russian army used a scorched-earth policy, and burned grain so the French could not use it as food. Napoleon took 420,000 men to take Moscow.
But once they got there, Moscow was already on fire. And it was Russia in the winter. So most of Napoleon's men died from the cold and he was left with 10,000 men. It was pretty much the worst attack plan of all time.
After Napoleon's three fatal mistakes, he was exiled. For a brief time, he escaped and returned to France for a hundred days of power before being exiled again. He died in exile, presumably of stomach cancer.