Necropolis in Olden Era is younger and hungrier than the cultivated death-cult that haunts later ages. The faction coalesced perhaps two centuries before the events of the game, when a circle of human and elven scholars in the eastern marshlands made a workable breakthrough in what would later be called formal necromancy — a discipline rather than a curse. They have been refining the method ever since, and they have been doing so in territory that no other power particularly wanted, which has bought them time.
The faction's identity is not nihilism. It is conservation. To a necromancer of this period, animating the dead is the only honest answer to a continent that consumes lives at industrial scale; the alternative is to let useful labor and useful knowledge rot in the ground. This argument is, naturally, not persuasive to the Temple, which considers the practice both a sin and a public-health hazard. The two factions are heading toward a war that everyone except the diplomats has already accepted.
Necropolis fields liches as administrators, vampires as field officers, and an enormous logistical advantage in the form of every casualty on every battlefield they win. Their magic emphasizes drain effects, curses, and the steady, grinding raise-chain that turns a near-loss into a strategic recovery.
For players, Necropolis is the snowball faction. Early it is fragile. Mid-game, if it has had any battles at all, it begins to compound. By month three an uncontested Necropolis is generally already over.