Boone served as syndic and commandant until 1804, when Missouri became part of the United States following the Louisiana Purchase. He was appointed captain of the local militia. Because Boone's land grants from the Spanish government had been largely based on oral agreements, he again lost his land claims. In 1809, he petitioned Congress to restore his Spanish land claims, which was finally done in 1814. Boone sold most of this land to repay old Kentucky debts. When the War of 1812 came to Missouri, Boone's sons Daniel Morgan Boone and Nathan Boone took part, but by that time Boone was much too old for militia duty.