Yet, the United States, despite guaranteeing the rights of former Mexicans to return to Mexico, developed legal arguments in order to institute formal barriers against this resettlement movement. The U.S. Secretary of War George W. Crawford even claimed that repatriation was prohibited. Because New Mexico served as the primary buffer between American settlers and indigenous groups, the U.S. believed it was in their best interest if the treaty citizens remained in the U.S. to maintain a “civilized” presence in the region and protect against Native encroachment.