One of the most serious weapons against napoleon's empire was

The English blockade of all trade with the European continent was one of the most important factors of Napoleon's downfall, thus making it one of the most powerful weapons against him. That, however, was not the only factor responsible for the collapse of his Empire. A part of it were personal factors. By this time, Napoleon had become overconfident, and one of the results of that was that he decided to invade Russia. This was a catastrophic mistake. Out of 600.000 men which set out on the campaing, only 25.000 returned. After the war, Russia has joined the blockade Britain had set up against France, which contributed to the weakening of Napoleon's Empire, and its downfall.