For America's 250th anniversary, which 1803 purchase nearly doubled the size of the United States?

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

The United States acquired the Louisiana territory from France through a treaty signed on April 30, 1803. The purchase price was $15 million, or roughly three cents per acre by later estimates. The territory covered about 827,000 square miles west of the Mississippi River, although its exact boundaries were not fully clear at the time.

President Thomas Jefferson authorized the deal after France offered to sell the entire territory rather than only New Orleans. The purchase gave the United States control of the Mississippi River and the port of New Orleans, both vital to western farmers and national commerce.

The acquisition created questions about constitutional authority, slavery, Native sovereignty, and the status of residents in the territory. The Lewis and Clark Expedition followed in 1804 to survey part of the new land and seek a route to the Pacific.