France decided to the sell the Louisiana Territory to us in 1803. The Louisiana Purchase doubled the size of country extending the land we controlled from the Atlantic Ocean, west to the Rocky Mountains, North to Canada, and South to the New Orleans and the border with Spanish Florida.
Napoleon was gearing up for a major war in Europe. While at one time Napoleon hoped to extend his control in North America, that was no longer an option by 1803. Napoleon really had no use for the land he controlled in North America. He also needed money to finance the war he would be fighting in Europe.
When the Americans approached with an offer to buy New Orleans and West Florida for $10 million, he decided to counter the offer with one of his own. He offered the entire Louisiana Territory to us for $15 million. While there was some hesitancy by President Jefferson to make the purchase because of constitutional concerns since President Jefferson didn’t believe the Constitution gave him the authority to buy land, President Jefferson was persuaded to agree to make the Louisiana Purchase and all of this land became American territory in 1803.