The midnight deal Robert Livingston, United States Minister to France, struck with French Finance Minister Francois Barbe-Marbois to purchase the Louisiana Territory was arguably the most impactful treaty in the history of the United States. While the purchase seemed like a gift from heaven, there were several significant issues with it. For one, the American commissioners were not authorized to purchase Louisiana; they had been instructed to purchase New Orleans and West Florida. Second, they had only been authorized to spend $10 million; they had exceeded that amount by half. Finally, there remained the legality of the purchase as the Constitution did not specifically grant the executive branch the power to purchase new lands.

When word leaked out that Spain had secretly agreed to transfer Louisiana and, possibly Florida, to France, the news hit like a thunderbolt. President Thomas Jefferson fully understood the significance of trading a weakened Spain for a powerful Napoleonic France as the country’s neighbor. In April 1802, Jefferson wrote to Robert Livingston, U.S. minister to France, to inform Napoleon, “There is on the globe one single spot the possessor of which is our natural and habitual enemy. It is New Orleans, through which the produce of three-eighths of our territory must pass to market.” Jefferson directed Livingston, who had been busy for months laying the foundation for the purchase of New Orleans, to warn Napoleon that France acquiring Louisiana “rendered it impossible that France and the United States can continue long friends.”

Because of several treaties in the 18th century, Spain controlled the entire west bank of the Mississippi and the east bank for a stretch of 150 miles, from Natchez to the Gulf of Mexico. Especially unfortunate for western Americans, Spain also controlled the river port of New Orleans, the key to the continent. The rapid influx of Americans into the region following the American Revolution became a great concern for Spanish officials, as the population of Kentucky and Tennessee grew tenfold, from 30,000 to 300,000, between 1784 and 1800.

In 1682, Robert de la Salle, a French explorer and fur trader, reached the mouth of the Mississippi River and claimed the interior of North America for King Louis XIV. Four decades later, Jean-Baptiste de Bienville founded New Orleans, creating a massive strategic arc across North America stretching from Quebec to the Gulf of Mexico. And from within this domain, the French controlled the core of the continent and the hugely profitable fur trade. But their hold did not go unchallenged and in a series of wars throughout the eighteenth century, the British dispossessed the French of its colonies in North America. As the final war drew to a close, France secretly transferred Louisiana and the river port of New Orleans to Spain rather than have Louisiana fall into British hands. When Napoleon came to power in 1799, he had visions of reestablishing a North American empire and in October 1800, he forced Spain’s King Carlos IV to give Louisiana back to France.