In 1803, with one bold move, President Thomas Jefferson's administration doubled the size of the United States. France's offer of the Louisiana Territory–828,000 square miles of land extending west of the Mississippi River, in exchange for $15 million–was simply too good to resist. The Treaty, dated April 30, 1803, was signed in Paris by Robert Livingston and James Monroe and ratified by Congress on October 20. Fifteen states or parts of states were carved from the vast territory, which was the single largest acquisition of land in U.S. history.

Sixteen years earlier, critics of the Constitution had argued that the original thirteen states already covered too vast a territory to be under a single government. In 1803, some European powers predicted that the huge addition of land would be the death knell of the American experiment and would cause the Union to degenerate into competing and warring factions. Jefferson, however, believed it would provide "a wide-spread field for the blessings of freedom." The Louisiana Territory added to the United States a wealth of natural resources beyond anyone's calculations. Westward expansion was a disaster for the many indigenous peoples who had no say in the sale of lands they had inhabited for generations. But the Louisiana Purchase did not weaken the Union; it strengthened it. The transaction was more than a brilliant act of diplomacy or a shrewd real estate deal. It was a vote of confidence in the future of a fledgling nation.