The Legion is first and foremost a slave army, the sole owner of which is Caesar. As Caesar conquers the peoples of the wasteland, he strips them of their tribal identities and merges them into his forces. There is no other tribe than the Legion itself.
As a slave army, the Legion maintains a very strict hierarchy or division of roles. All able-bodied males become slave soldiers with a singular purpose: to fight for Caesar until they fall in battle. This reason for being is imprinted into each legionary during his reconditioning, or, if one was born into the Legion, upbringing and training. Legionaries become unconditionally devoted to their leader, living to fight. Contrary to expectations, experience and veterancy has no bearing on one's position in the Legion. While some may receive better equipment and more dangerous tasks to fulfill, at the end of the day, all soldiers remain slaves, disposable human tools that are discarded the moment they stop fulfilling their purpose.
Women are given the role of, essentially, support corps. Caesar specifically forbids women from fighting, instead using them as caretakers, healers, midwives, and breeders to support the Legion's continuous campaign of expansion. Almost all members of the Legion express condescending and downright misogynistic opinions of women and their non-combat roles. While the portrayal of female slaves in Fallout: New Vegas follows standard stereotypes, it is important to reiterate that both females and males in the Legion are fully subjugated by Caesar - though women have the distinction of being considered 'sub-human' instead of merely slaves, due to the Legion's perception of their sex.