The United States purchased the Louisiana Territory from France in 1803, which effectively doubled its size. This acquisition, known as the Louisiana Purchase, took place during President Thomas Jefferson's administration and involved the purchase of over 828,000 square miles of land west of the Mississippi River. The deal was made for approximately $15 million, which at the time was a substantial sum. The purchase was significant not only for its geographic expansion but also for its implications for westward expansion and the growth of the United States as a continental power. It paved the way for exploration, settlement, and development of the American West.