Relations break down between Wakanda and the DC United States of America. The result is WAR.
The scenarios are:
1) DC USA forces invade Wakanda
2) Wakandan forces invade DC USA
3) Battle it out over neutral ground
Each side gets standard government & military forces and tech as depicted in their respective universes.
For superhumans/metahumans, each country can only call on those characters who are shown as regularly in service or hire of the governments and military eg. DC USA gets guys like Wraith and Suicide Squad, but they can't call up guys like Superman, Batman etc.
Version is up to you... Preboot, DCnu, President Luthor era USA etc.
Aside from the affore me tioned Suicide Squad, there is the other branches of Task force X, the conglomerate, the metal men (depending on when in DCU history we take it from), the Doom patrol (also dependant on time in continuity, and the freedom fighters in some versions. Then there's Captain Atom, Major Force, General glory,...................... do I really need to go on? (Because I'm far from done).
Then we have to consider to we allow all the checkmate tech, the promethium armor and weapo s developed by Dayton Industries for the US (that was actually how Steve Dayton- ah la Mento got himself on the Doom Patrol and close to his love interest elastic Girl. By using his weight with the US military to get him added), the Omac's etc.
Not really seeing this as fair if we allow metas. With just tech and conventional forces yes but not metas
DCnU USA also has/had the JLA on payroll (I haven't kept up since the beginning) and Argus has collected a shitload of tech and magical artifacts in their variously colored rooms.
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"And then there was nothing. A once broken something now void.
And on the first day, Doom spoke... 'Be.'
And then there was life."
wakanda has actually beaten latveria before, their technology is far beyond Atlantis' and their defenses would repel them (let's not forget that they have dozens of weapons that are made specifically for fighting atlanteans), and panther and bolt are best friends, they wouldn't go to war.