Louisiana Purchase, the purchase of the French province of Louisiana by the United States in 1803. The province stretched from the Mississippi River westward to the Rocky Mountains and from the Gulf of Mexico northward to Canada, covering an area roughly equal to that of the United States prior to the purchase. Except for the Mississippi River on the east and Canada on the north, the boundaries were indefinite. The United States also claimed West Florida between the Mississippi and Perdido rivers as part of the purchase, but Spain denied the claim.
As a result of the purchase, the port of New Orleans and the entire Mississippi River system were secured for American shippers, and the country was free to expand toward the Pacific Ocean. The price was $15,000,000 for an area of 828,000 square miles (2,145,000 km 2 )—less than three cents an acre.
In 1762 France ceded the region beyond the Mississippi to Spain by the Treaty of Fontainebleau (confirmed by the Treaty of Paris of 1763). This was to compensate the Spanish for being allied to France in the Seven Years' War. In 1800, however, Napoleon got Spain to return it by a secret treaty. Napoleon planned a French empire in the New World, with its center at New Orleans. President Jefferson was alert to the dangers of a powerful nation controlling the mouth of the Mississippi. He instructed the American minister to France, Robert R. Livingston, to open negotiations to buy New Orleans and some territory east of the city.
Livingston's difficulties were great. He had to deal with Talleyrand, the wily French foreign minister. The boundaries of the province were uncertain. A treaty would have to satisfy the financial claims that some United States citizens had against the French government. Finally, the French continued to claim that the province still belonged to Spain. Jefferson sent James Monroe to help with the negotiations and authorized him to spend up to $10,000,000.
Meanwhile, Napoleon's plans for an American empire had been shattered. The large army he sent to the Caribbean island of Hispaniola to subdue Toussaint L'Ouverture was destroyed by an epidemic of yellow fever and attacks by Haitian guerrillas. Threatened with a new war in Europe, Napoleon suddenly offered Livingston and Monroe the entire province of Louisiana. In a treaty dated April 30, 1803 (but signed May 2), the American negotiators agreed to pay $11,250,000 to France and $3,750,000 for the French debts to United States citizens.
The purchase forced Jefferson to give a broad interpretation to the Constitution, which did not specifically grant authority for acquiring new territory. This interpretation set the precedent for later treaties that added to United States territory.
The U.S. Senate promptly ratified the purchase treaty, despite political opposition by the Federalists. The area officially became United States territory on December 20, 1803. However, it was 16 years before the exact boundaries were established, by the Adams-Onís Treaty with Spain. Thirteen states were eventually created, in whole or in part, out of French Louisiana: Louisiana, Missouri, Arkansas, Iowa, Minnesota, Kansas, Nebraska, Colorado, North Dakota, South Dakota, Montana, Wyoming, and Oklahoma.