You may win the game by conquest if you eliminate all remaining factions. Factions which surrender and “swear a pact to serve you” count as eliminated for this purpose. If Cooperative Victory is enabled, you need not eliminate any faction with whom you have signed a Pact, though aside from surrendered AI factions no more than three factions may “win together” in this fashion.
For winning by Conquest, you are awarded 1000 points minus 2 for every game turn elapsed. If Cooperative Victory is enabled and more than one faction survives the game, the points are split between them based on relative population.