What was the largest land acquisition in United States history when completed in 1803?

The Louisiana Purchase was the largest land acquisition in United States history when completed in 1803.

The United States acquired the territory from France through a treaty signed on April 30, 1803, and formally transferred it later that year. The purchase covered about 828,000 square miles west of the Mississippi River, extending from the river toward the Rocky Mountains and from the Gulf of Mexico toward the Canadian border.

President Thomas Jefferson authorized negotiations after France regained control of Louisiana from Spain. The United States initially sought New Orleans and navigation rights on the Mississippi, but French leader Napoleon Bonaparte offered the entire territory. The agreement cost 15 million dollars, or roughly three cents per acre by contemporary calculations.

The purchase nearly doubled the nation’s size, but its boundaries and the exact lands included were debated. The later exploration of the region by the Lewis and Clark Expedition helped the United States map and study its new western territory.