I'm placing the Atlanteans Tech at around a millenium years more advanced then the rest of the world, especially since Europe, since they were leading the way with technology at this point of time. The Atlantians have rifles, battleships, semi power-armor, maybe even Mechs? I haven't decided on what gear the Atlantians properly have yet, but it's more then enough to curb stomp pretty much anything that dares take arms against it. They are still mortal men however, and can be killed. If the human resistance were to mass-produce these weapons somehow, then the playing field would be even to some degree. Also, are you guys happy for a time-skip?
I'd prefer we didn't jump ahead this early on. The characters don't even know each other's names yet.