What 1803 transaction greatly expanded the United States, a major event in the country's 250-year story?

The Louisiana Purchase was the 1803 transaction in which the United States acquired a vast territory from France.

The United States agreed to pay France $15 million, including the assumption of certain claims by American citizens. The purchase covered about 828,000 square miles, although its exact boundaries were initially uncertain. It roughly doubled the size of the United States.

President Thomas Jefferson authorized the negotiations, and Robert Livingston and James Monroe concluded the agreement with France. Napoleon Bonaparte’s government agreed to sell partly because renewed war in Europe made it difficult for France to maintain its North American holdings.

The purchase led to exploration by the Lewis and Clark Expedition, which began in 1804. It also raised major questions about Indigenous sovereignty, slavery’s expansion, and the future organization of western territories. The Louisiana Purchase is distinct from the Alaska Purchase, completed in 1867, and the Gadsden Purchase, completed in 1854.