The Louisiana Purchase of 1803 was the transfer of the western half of the Mississippi Valley from Spain and France to the United States. It encompassed 900,000 square miles of fertile lands, inhabited by Indian tribes, a few thousand French settlers and a rapidly growing population of American frontiersmen. It represented the single most important territorial acquisition by the United States during its transcontinental development. It was purchased by President Thomas Jefferson, who stretched the Constitution to do so. Napoleon, the ruler of France was eager to sell it for $15,000,000; Spain had no choice in the matter. The Purchase contained most of what is now the west central section of the United States.
In 1762, the French province of Louisiana included the Ohio and Mississippi valleys and the shore line of the Gulf of Mexico both east and west of the Mississippi. France lost it after the French and Indian War (Seven Years War) in 1763. The peace treaty gave Spain New Orleans and all the lands west of the Mississippi; the British took the lands east of the Mississippi. By 1800 Napoleon, with dreams of a new French Empire in the Caribbean, sensed the strategic importance of Louisiana and decided to take it from Spain. By the Treaty of San Ildefonso, Oct. 1, 1800, and the Convention of Aranjuez, Mar. 21, 1801, Napoleon acquired Louisiana for France in return for placing the son-in-law of the Spanish king on the newly erected throne of Etruria.
Rumors of this secret retrocession from Spain to France reached the United States, causing apprehension of possible encirclement. President Jefferson said that America was faced with the prospect of "marrying the British fleet and nation" (that is, becoming an ally of Britain in the large-scale wars underway between Britain and France) as an offset to this new French empire in the heart of the continent. Livingston and special envoy James Monroe in Paris plied the French with arguments for a deal with the United States as they strove to buy just the coastal areas of New Orleans and West Florida. In the final decision to sell the whole province of Louisiana to the Americans, Napoleon was influenced by the imminent renewal of war with Britain, when Louisiana might be lost anyway, and the consequent need for money as well as by the failure of his Haitian campaign, where his invasion army had been destroyed by disease. Napoleon's chief goal was to strengthen the United States as a counter-weight to Britain.
Exceeding their instructions, the American envoys accepted Napoleon's offer. By a treaty and two conventions, all dated April 30, 1803, the United States paid $11.25 million for Louisiana, set aside $3.75 million to pay the claims of its own citizens against France, and placed France and Spain on an equal commercial basis with the United States in the colony for a period of twelve years. To finance the sale the U.S. delivered Treasury bonds to France, which it immediately resold to British bankers for gold. On November 30, 1803, Spain formally delivered the colony to the French colonial prefect, who on December 20, 1803, officially transferred the territory to the American commissioners.
It was important to the growing United States that Americans could gain access to the vast interior of North America via the Mississippi River and the port of New Orleans. The nation recognized the bargain, but some Republicans complained that the Constitution did not allow such a purchase, and many Federalists were alarmed that eventually the western population would overwhelm their stronghold in the Northeast. Congress voted approval and voted the funds. The acquisition provoked several reversals of policy as Federalists and Jeffersonian Republicans competed for electoral preeminence. Federalists had long ignored or disparaged the Western frontier, but they soon saw that their future depended on expanding their electoral strength beyond the Northeast. Their support for access to the Mississippi River and the acquisition of New Orleans and other territories largely rested on their need to remain competitive with their Republican rivals. Republicans, on the other hand, sensed their growing strength in the South and West and relaxed their narrower reading of the Constitution to argue for the purchase, even though it would increase the power of the government.
The region was poorly mapped. All that the Republic could be certain of in 1803, however, was that it had acquired a corridor down the Mississippi River to the Gulf of Mexico, the width of which was uncertain. The great exploring expedition of Lewis and Clark revealed the extent and riches of the vast territory.
Later treaties by John Quincy Adams in 1818 and 1819, with Britain and Spain set the boundaries. The Treaty of 1818 placed the nation's northern boundary (with present-day Canada) along the forty-ninth parallel from the Lake of the Woods to the Rocky Mountains and excluded the British altogether from the Mississippi Valley. The right to this valley and its great tributaries in the West, including the Spanish claim to Oregon, was won in the Treaty of 1819 by drawing the western boundary up the Sabine, Red, and Arkansas rivers to the Rocky Mountains and then westward along the 42nd parallel to the Pacific.
The acquisition of this enormous tract laid a large part of the material foundation for the future greatness of the United States. More immediately, however, its possession ensured the right of free navigation of the Mississippi and the control of the port of New Orleans, vital to western trade, as an integral part of American territory. Moreover, it reinforced the security of the new republic by eliminating France in the contest for supremacy in North America.
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- In 1763 the British also took control of Florida from Spain; in 1783 the British returned East Florida and West Florida to Spain.