I solemnly swear to devote my life and ability in the defense of the United Nations of Earth, to defend the constitution of man, and to further the universal rights of all sentient life, from the depths of the Pacific, to the edge of the galaxy, for as long as I shall live.

That is the pledge of the UNE, the United Nations of Earth, said by all service members in its military. He is in the UNE’s army, specialized in combat on the solid ground of nearby and distant planets. The Solar System became a melting pot of different sentient species as the UNE, and humans themselves took a more peaceful approach in first contact. He is in the barracks on a base on Earth, reading his favorite book, an autobiography written by one of the first astronauts on Mars in the 21st century.