Excerpts from Books and Wikipedia
"The Adams–Onís Treaty (...) of 1819, also known as the Transcontinental Treaty, the Florida Purchase Treaty, or the Florida Treaty, was a treaty between the United States and Spain in 1819 that ceded Florida to the U.S. and defined the boundary between the U.S. and New Spain. It settled a standing border dispute between the two countries and was considered a triumph of American diplomacy. It came in the midst of increasing tensions related to Spain's territorial boundaries in North America against the United States and Great Britain in the aftermath of the American Revolution; it also came during the Latin American wars of independence. . . . Adams was deeply interested in establishing American control over the Oregon Country, partly because he believed that control of that region would spur trade with Asia. The acquisition of Spanish claims to the Pacific Northwest also allowed the Monroe administration to pair the acquisition of Florida, which was chiefly sought by Southerners with territorial gains favored primarily by those in the North." [Wikipedia]