Napoleon was a masterful ruler. He established a number of reforms that brought peace and stability back to France. He also rewrote the old French feudal laws, which were confusing, creating a new Napoleonic Code of laws that were much clearer. Many of these laws remain in France to this day.
After bringing economic prosperity and peace to France, Napoleon set out to conquer the remainder of Europe. As a skillful general, he was able to conquer significant tracts of land.
By 1812, Napoleon controlled most of Europe, either directly or indirectly.