At the time of Glanton’s contact with Mangas relative peace between the U.S. Government and the Apache was still in existence, In 1846, when the United States went to war with Mexico, the Apache Nation had promised U.S. soldiers safe passage through Apache lands, and after the U.S. occupation of New Mexico, Mangas Coloradas signed a peace treaty, recognising them as conquerors of the Apache’s Mexican enemies. However, a number of crimes perpetrated against the Apache by the Americans over the next decade would eventually lead Mangas to join with Cochise in a bid to drive the Americans out of Apache territory.
Even within the long history of American mistreatment of Native Americans, the eventual fate of Mangas was especially shameful. In January 1863, Mangas arrived under a flag of truce to meet with U.S. military leaders at Fort McLane, New Mexico, to call for peace. He was immediately taken into custody by armed guards. Later that night he was murdered. The following day, his head was cut off, boiled and the skull sent to a New York City phrenologist.