Jackson had first gotten to know Burr in 1805 when he stayed with the Jacksons at the Hermitage during a tour of what was then the Western United States that he had embarked on after mortally wounding Alexander Hamilton in the Burr–Hamilton duel.[66] Burr eventually persuaded Jackson to join his adventure. In October 1806, Jackson wrote James Winchester that the United States "can conquer not only the Floridas [at that time there was an East Florida and a West Florida], but all Spanish North America".[67] He informed the Tennessee militia that it should be ready to march at a moment's notice "when the government and constituted authority of our country require it",[68] and agreed to provide boats and provisions for the expedition.[66] Jackson sent a letter to president Thomas Jefferson telling him that Tennessee was ready to defend the nation's honor.[69]
Jackson also expressed uncertainty about the enterprise. He warned the Governor of Louisiana William Claiborne and Tennessee Senator Daniel Smith that some of the people involved in the adventure might be intending to break away from the United States.[70] In December, Jefferson ordered Burr to be arrested for treason.