He then founded the American Association of Mexico (AAM), a lobby group working to amend Article 27 of the 1917 Mexican Constitution to remove recent restrictions on individual American ownership of land and oil rights. In 1921, the Mexican government expelled Buckley because of his AAM activity. Buckley reported on his expulsion to the Secretary of State of the United States in 1922. He donated his papers to the University of Texas in 1923. In 1924, Mexican President Plutarco Elías Calles invited Buckley to return to Mexico, but instead he transferred his Pantepec Oil Company to Venezuela.