In one of the great surprises in diplomatic history, French Foreign Minister Charles Maurice de Talleyrand makes an offer to sell all of Louisiana Territory to the United States.

Talleyrand was no fool. As the foreign minister to French Emperor Napoleon Bonaparte, he was one of the most powerful men in the world. Three years earlier, Talleyrand had convinced Napoleon that he could create a new French Empire in North America. The French had long had a tenuous claim to the vast area west of the Mississippi River known as Louisiana Territory, which had already been occupied by Native Americans for centuries. In 1800, Napoleon secretly signed a treaty with Spain that officially gave France full control of the territory. Then he began to prepare France’s mighty army to occupy New Orleans and bolster French dominion.

When President Thomas Jefferson learned of Napoleon’s plans in 1802, he was understandably alarmed. Jefferson had long hoped the U.S. would expand westward beyond the Mississippi, but the young American republic was in no position militarily to challenge France for the territory. Jefferson hoped that his minister in France, Robert Livingston, might at least be able to negotiate an agreement whereby Napoleon would give the U.S. control of New Orleans, the gateway to the Mississippi River.

At first, the situation looked bleak because Livingston’s initial attempts at reaching a diplomatic agreement failed. In early 1803, Jefferson sent his young Virginia friend James Monroe to Paris to assist Livingston. Fortunately for the U.S., by that time Napoleon’s situation in Europe had changed for the worse. War between France and Great Britain was imminent and Napoleon could no longer spare the military resources needed to secure control of Louisiana Territory. Realizing that the powerful British navy would probably take the territory by force, Napoleon reasoned it would be better to sell Louisiana to the Americans than have it fall into the hands of his enemy.

After months of having fruitlessly negotiated over the fate of New Orleans, Livingston again met with Talleyrand on this day in 1803. To Livingston’s immense surprise, this time the cagey French minister coolly asked, “What will you give for the whole?” He meant not the whole of New Orleans, but the whole of Louisiana Territory. Quickly recognizing that this was an offer of potentially immense significance for the U.S., Livingston and Monroe began to discuss France’s proposed cost for the territory. Several weeks later, on April 30, 1803, the American emissaries signed a treaty with France for a purchase of the vast territory for $11,250,000.

A little more than two weeks later, Great Britain declared war on France. With the sale of the Louisiana Territory, Napoleon abandoned his dreams of a North American empire, but he also achieved a goal that he thought more important. “The sale [of Louisiana] assures forever the power of the United States,” Napoleon later wrote, “and I have given England a rival who, sooner or later, will humble her pride.”