Mercenary

Mercenary from Tomorrow is a 1968 science fiction novel written by Mack Reynolds. It is the first in a series about Joe Mauser, a soldier in a rigid, caste-based society that makes it very difficult to better oneself. Western society is split up into nine castes, from Lower-Lower to Mid-Lower all the way up to the privileged Upper-Upper. Mauser himself was born a Mid-Lower. Ambitious, he had chosen one of the few professions, Category Military, where upward mobility was still a reasonable possibility.