The Continental System: The Continental System is a decree that ordered a blockade that closed ports to prevent trade and communications between Great Britain and other European countries. It was named this because it was supposed to make continental Europe more self-sufficient. Napoleon's blockade wasn't tight enough which allowed smugglers to bring cargo from other countries. The Continental System hurt France's economy and other countries under his control more than it hurt Britain.
The Peninsular War: Napoleon sent an army through Spain to invade Portugal because they ignored the Continental System. Spanish towns had riots which resulted in Napoleon deposing the Spanish king and putting his brother on the throne. This outraged the Spaniards because they were really loyal to their former king. Napoleon lost over 300,000 men during the war, which only weakened the French Empire. Other enemies started to become a powerful weapon against Napoleon after this.
This was Napoleons biggest mistake. French ans Russian rulers saw each other as having competing designs on Poland which caused a breakdown in their alliance. Napoleon then decided to invade Russia. His troops had very little loyalty to Napoleon. The Russians burned all grain fields and killed all of their livestock so their enemy would have nothing to eat. This caused soldiers to desert the army to search for food. Alexander torched Moscow instead of surrendering it and Napoleon stayed there for weeks, waiting for a peace offering from the czar, but nothing came. Napoleon ordered his starving men to turn back. The snow started to fall and the temperature fell by 30 degrees. There were only 10,000 soldiers left fit to fight after survivors left Russia.