Thomas Jefferson claimed that Louisiana stretched west to the Rocky Mountains and included the entire watershed of the Mississippi and Missouri Rivers and their tributaries, and that the southern border was the Rio Grande. Spain maintained that Louisiana extended only as far as Natchitoches, and that it did not include the Illinois Territory. Texas was again considered a buffer province, this time between New Spain and the United States. The disagreement would continue until the signing of the 1819 Adams–Onís Treaty, at which point Spain gave Florida to the United States in return for undisputed control of Texas.