What 1803 acquisition greatly expanded the territory of the United States?

The Louisiana Purchase was the 1803 acquisition that greatly expanded United States territory.

The United States agreed to buy Louisiana from France in a treaty signed on April 30, 1803. The purchase covered about 828,000 square miles west of the Mississippi River, including land reaching toward the Rocky Mountains.

The United States paid France $15 million, or roughly three cents per acre. President Thomas Jefferson supported the deal because control of the Mississippi River and New Orleans was vital to western farmers and national commerce.

The purchase nearly doubled the size of the United States, although its exact boundaries were not immediately clear. The Lewis and Clark Expedition, launched in 1804, helped explore the newly acquired territory and map routes toward the Pacific.