But the greatest irony of Jefferson’s presidency involved his greatest achievement, the Louisiana Purchase. This resulted not from astute American diplomacy but because the rebellious slaves of Saint Domingue defeated forces sent by the ruler of France, Napoleon Bonaparte, to reconquer the island. Moreover, to take advantage of the sudden opportunity to purchase Louisiana, Jefferson had to abandon his conviction that the federal government was limited to powers specifically mentioned in the Constitution, since the document said nothing about buying territory from a foreign power.

This vast Louisiana Territory, which stretched from the Gulf of Mexico to Canada and from the Mississippi River to the Rocky Mountains, had been ceded by France to Spain in 1762 as part of the reshuffling of colonial possessions at the end of the Seven Years’ War. France secretly reacquired it in 1800. Soon after taking office, Jefferson learned of the arrangement. He had long been concerned about American access to the port of New Orleans, which lay within Louisiana at the mouth of the Mississippi River. The right to trade through New Orleans, essential to western farmers, had been acknowledged in the Treaty of San Lorenzo (also known as Pinckney’s Treaty) of 1795 between the United States and Spain. But Jefferson feared that the far more powerful French might try to interfere with American commerce. He dispatched envoys to France offering to purchase the city. Needing money for military campaigns in Europe and with his dreams of American empire in ruins because of his inability to reestablish control over Saint Domingue, Napoleon offered to sell the entire Louisiana Territory. The cost, $15 million (the equivalent of perhaps $250 million in today’s money), made the Louisiana Purchase one of history’s greatest real-estate bargains.

White Hall Plantation, painted around 1800, depicts a Louisiana plantation and the dynamism of the region’s economy on the eve of its acquisition by the United States. Black oarsmen man a boat carrying bales of cotton for sale in New Orleans.

The Louisiana Purchase of 1803 doubled the land area of the United States.

In a stroke, Jefferson had doubled the size of the United States and ended the French presence in North America. Federalists were appalled. “We are to give money, of which we have too little,” one declared, “for land, of which we already have too much.” Jefferson admitted that he had “done an act beyond the Constitution.” But he believed the benefits justified his transgression. Farmers, Jefferson had written, were “the chosen people of God,” and the country would remain “virtuous” as long as it was “chiefly agricultural.” Madison, in Federalist no. 10, had explained that the large size of the republic made self-government possible—“extend the sphere,” he had proclaimed. Now, Jefferson believed, he had ensured the agrarian character of the United States and its political stability for centuries to come.

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