In 1803 went Jefferson was president the federal government bought a vast territory west of the Mississippi from France. That land belongs to the federal government, the feds paid for it. Alaska was bought from the Russians in 1867 so the feds own Alaska too. As a result of the Mexican American war the federal government "bought" from Mexico most of the US south west that too belongs to the federal government.
Texas is unique in that it has a legitimate claim to the right of secession since it entered the union via treaty as an independent republic.