The Louisiana Purchase was the 1803 acquisition from France that nearly doubled the territory of the United States.
President Thomas Jefferson’s administration agreed to buy the vast Louisiana territory for $15 million. The treaty was signed on April 30, 1803, and the United States formally took possession later that year. The purchase covered land west of the Mississippi River and included the important port of New Orleans.
The transaction was made possible partly because Napoleon Bonaparte had abandoned plans for a major French empire in North America. The exact boundaries were initially uncertain, and later exploration helped the United States map and claim the new territory. The Lewis and Clark expedition, launched in 1804, became one of the best-known government projects connected with the purchase.
The acquisition expanded the nation by roughly 828,000 square miles, although it also intensified disputes over Indigenous sovereignty, slavery, and the future balance between free and slave states. It is often described as the largest territorial expansion in United States history completed through a single purchase.