The significant land acquisition in 1803 that doubled the size of the United States was the Louisiana Purchase. This deal was negotiated between President Thomas Jefferson and France, acquiring approximately 828,000 square miles of territory for $15 million. The purchase significantly increased the nation's land area, facilitated westward expansion, and was driven by the vision of an agrarian society. The Louisiana Purchase also sparked debates over slavery and the rights of indigenous peoples, setting the stage for future conflicts and the creation of new states.