Star soldiers

the long version

The galactic civilization that considered Earthmen fit only to be their mercenaries in their constant conflicts - and Earthmen were not allowed to go into space in any other role - which wound up with the Earthmen rebelling against the galactic oppressors. After long centuries the last vestiges of the Galactic Union is falling apart and Earthmen are out to make their own stamp upon the galaxy In doing so, one underfunded ship lands on a new world that seems weirdly strange and familiar at the same time. A good read.