Black Panther and the forces of Wakanda
Namor and the forces of Atlantis
A war has broken out between Wakanda and Atlantis. T'Challa and Namor each want to take over the other's kingdom, so they'll try to cause as little collateral damage as possible, but other than that this is all out war. Both kings have all the resources and armies in their kingdoms, but T'Challa doesn't have Storm. There will be no outside interference. Everyone is in character, save for fighting each other, obviously.