On the contrary, conscription, and armies consisting of the population of a country in general (as opposed to mercenary armies) are a democratic achievement of (among a few other factors) the French Revolution.

In the actual times of slavery, e.g. in Ancient Greece and Rome it was free men that first and foremost did the fighting (and who considered it their honor and what made them and kept them free), and in the dark medieval times of peasants, feudal lords used mercenary armies (including against their subjects).

Conscription appeared on the scene as a way to have the army be controlled more by the population -- as opposed to it being professional soldiers ready to be used against the people.