Because he was heavily defeated at the Battle of Waterloo near Brussels in 1815 by the combined British and Prussian armies and sent into exile for a second time. This time he was sent to St Helena in the middle of the Atlantic Ocean away from all his family.
While the Battle of Waterloo was what finally made Napoleon lose power, there were several other reasons leading up to it, most notably:
- A disastrous campaign in Russia, in which Napoleon lost half a million men and 200,000 horses.
- Napoleon's poor choice of king in Spain, his brother Joseph. While Joseph was a well meaning ruler, he was not a competent man for the job, and could not deal with the difficulties and immense pressures of ruling the riotous Spanish people. As a result of this, the British managed a successful campaign through Spain and up to southern France.
- When Napoleon made himself emperor, many of his previous supporters began to lose faith in, as the new position made Napoleon more comparable to the Bourbon Dynasty who had ruled France in the past. A dynasty the revolution had striven so hard to get rid of.
