The action that best completes the graphic organizer is:
"The U.S. agrees to give Texas back to Mexico to avoid further fighting."
This action would logically fit into a sequence of territorial changes and agreements between the U.S. and Mexico, although it is historically inaccurate, as the U.S. did not give Texas back to Mexico after its annexation. However, if the focus is on actions between the two nations regarding territorial disputes, it completes the theme of territorial exchanges and conflicts.