Napoleon sold Louisiana to the United States because at that time in the early 1800s, France was in a bitter war with surrounding European nations and suffered large amounts of debt from Napoleon's tyrannous rule. He didn't have enough troops to secure France during these wars while at the same time shipping more troops to America to govern Louisiana. Also with Spanish territories to the American west and the U.S. to the east it was difficult for Napoleon to enter into Louisiana due to America taking over the Mississippi River. As a result, he had no choice but to annex the Louisiana Territory to Thomas Jefferson for a cheap amount of 15 million dollars ~ roughly 10 ¢ per acre.