The Louisiana Purchase expanded the United States in 1803, a major event in America250 history.
The United States acquired the Louisiana Territory from France through a treaty signed on April 30, 1803. The agreement transferred about 828,000 square miles of land west of the Mississippi River for $15 million.
President Thomas Jefferson supported the purchase because control of New Orleans and the Mississippi River was important to western farmers and national trade. The purchase roughly doubled the size of the United States and created opportunities for future settlement and exploration.
The transaction did not instantly settle every boundary question. The territory’s limits were debated, and the acquisition also intensified conflicts over Indigenous lands and the expansion of slavery. The Lewis and Clark Expedition began in 1804 to explore parts of the newly acquired region.