What 1803 acquisition nearly doubled the territory of the United States?

The Louisiana Purchase nearly doubled the territory of the United States in 1803.

The United States acquired the Louisiana Territory from France through a treaty signed on April 30, 1803. The agreement covered about 828,000 square miles, extending from the Mississippi River toward the Rocky Mountains and from the Gulf of Mexico northward. The United States paid $15 million, including the assumption of certain claims by American citizens.

President Thomas Jefferson supported the purchase because control of the Mississippi River and the port of New Orleans was vital to western farmers and merchants. The transaction also removed France from a major position in mainland North America. Congress approved the treaty, and the formal transfer took place in December 1803.

The purchase did not instantly create all the modern states in the region. Much of the territory was later surveyed, organized into territories, and admitted as states over many decades. It also involved lands inhabited by numerous Indigenous nations, whose sovereignty was not represented in the treaty negotiations.