The Louisiana Purchase was one of the greatest diplomatic accomplishments in American history, a peaceful and cheap acquisition of territory that doubled the size of the United States and enabled its transcontinental destiny. Ironically, the Purchase occurred through no great feat of negotiation or careful treaty-making, but almost as an accident—what Thomas Jefferson called "a fugitive occurrence."9
In 1803, Jefferson dispatched his emissaries Robert Livingston and James Monroe to Paris not to purchase half a continent but only to seek to guarantee American access to the vital port of New Orleans. At the turn of the nineteenth century, roads were rudimentary and railroads had not yet been invented; water transport was the only realistic option for long-distance commerce. Thus, Americans pushing westward through the Appalachian Mountains were entirely dependent upon the Mississippi River and its tributaries if they wished to ship their produce to faraway markets. If the Spanish or French rulers of New Orleans, near the mouth of the Mississippi, shut off American use of the port there, American farmers in the Mississippi Valley would be completely cut off from the market.
When Napoleon gained control of Louisiana after 1800, Jefferson feared a closure of the port would provide "the embryo of a tornado which will burst on the countries on both sides of the Atlantic and involve in its effects their highest destinies."10 In other words, French restriction of American access to New Orleans would have led to an almost-irresistible clamor for war among Americans in the West—and war against Napoleon was the last thing Jefferson wanted.
Hence Jefferson sent Livingston and Monroe on their urgent mission to Paris to attempt to buy New Orleans outright, or if Napoleon proved unwilling to sell, at least to purchase American rights to access the port. Little did Jefferson, Livingston, or Monroe know that Napoleon's losses in Haiti had caused him to abandon his plans for empire on the American mainland altogether. When Napoleon's ministers made an unsolicited offer to sell the entire Louisiana Purchase to the Americans, Livingston and Monroe jumped to seize the opportunity—despite the fact that they had been authorized to make no such purchase and that Jefferson himself believed that such a purchase was unconstitutional.
In the end, the Louisiana Purchase was not so much a shrewd bargain on the part of the Americans as a virtual gift to the fledgling American republic from Napoleon Bonaparte. (Or perhaps, more accurately, from the freed Haitian slaves.)