Let’s come up with new “war machines.”

If you're fighting against the Academy, use sappers; against the Sylvan, use gardeners; against the Warlock, use electricians; against the Necropolis, use gravediggers (this is all in the context of sieges):D :D :D :D
And I would create unique siege engines for each faction (for example: elves, as they don't like machines and all sorts of dark technology (see the faction description), could make an ENT instead of a catapult, which would throw stones (like a catapult against walls), and instead of a ballista, I don't know what else could be invented, etc. By the way, like in Warcraft, you could let the Necropolis use a corpse cart as a catapult!