One of the dramatic episodes in the building of American power occurred in 1803. France sold the immense territory of Louisiana to the United States. Roughly 828,000 square miles were ceded at a cost of $15 million (four cents an acre), thereby doubling the size of US holdings. Despite haziness in Washington and Paris about the precise placement of Louisiana's borders, they encompassed – according to US definition – most of the land between the Mississippi river and Rocky mountains.

This acquisition accomplished several things simultaneously. It reconfirmed the expulsion of French power from North America, which even the audacity of Napoleon III's Mexican project would not later reverse (or Charles de Gaulle's verbal solidarity with Quebec vitiate). Louisiana's transfer also eliminated the buffer zone between the United States and New Spain, imperiling Madrid's weak grip on such remote provinces as California, Texas, and Mexico. Additionally, this purchase smoothed the way for subsequent US expansion westward to the Pacific. The Empire of Liberty, Thomas Jefferson's construction of the US republic, thus achieved in a single stroke bloodless conquest and sturdy claim to future eminence.

The overwhelming majority of Americans in 1803 was elated. Pundits, Republican newspaper editors, and popular demonstrations greeted the annexation with praise. They called it noble, glorious, sublime. Andrew Jackson, then a judge on the Tennessee superior court and major general in the state militia, reported to President Jefferson: “Every face wears a smile, and every heart leaps with joy.”