The Adams-Onís Treaty (also called the Trans-Continental Treaty) of 1819 settled the boundary between the United States and the Spanish Empire. It sold Florida to the Americans in exchange for a boundary that removed claims still lingering from the Louisiana Purchase of 1803. Many of the present-day outlines of Texas begin to take shape from this treaty, including the Sabine River, the 32° line of longitude to the Red River, then 100° longitude to the Arkansas River.
Not every American approved of this new arrangement. Many insisted that the brief forays made by the French in the region, starting with that of René-Robert Cavelier, Sieur de La Salle in the 1680s, put most of Texas in with the Louisiana Purchase. These citizens saw the treaty as a surrender on the part of the US government, and several plotted ways to get Texas out of the Spanish sphere once and for all.