Divergent

From the text:

Marcus is my father’s coworker; they are both political leaders. The city is ruled by a council of fifty people, composed entirely of representatives from Abnegation, because our faction is regarded as incorruptible, due to our commitment to selflessness. Our leaders are selected by their peers for their impeccable character, moral fortitude, and leadership skills. Representatives from each of the other factions can speak in the meetings on behalf of a particular issue, but ultimately, the decision is the council’s. And while the council technically makes decisions together, Marcus is particularly influential. It has been this way since the beginning of the great peace, when the factions were formed. I think the system persists because we’re afraid of what might happen if it didn’t: war.

Why were the factions created in the first place? Why does this system continue?