Why did Spartacus leave the Roman Army?
Spartacus never served in the Roman army. Simply because only Roman citizens could serve as soldiers and no Roman citizen could become a slave- regardless of the crime. They might face execution or deportation – but never slavery From what we know of Spartacus- he was a “first generation” slave- meaning he was born free and enslaved afterwards. Quite possibly he became a slave as the result of being a prisoner of war (extremely common at that time). Assuming he was an adult at the time of capture he most likely had military experience (every male at the time had some training). He might have been even a minor leader of his people before capture (important leaders were executed by the Romans) so he knew how to organise a group of fighters.
