An illegal transaction between citizens of Atlantis and Wakanda. The deal involves illegal purchase by Atlanteans of Wakandan technology. The deal isn't going well at all, the Wakandans want to increase the agreed upon price citing increased risk. The Atlanteans will have none of it. Suddenly, 'increased risk' is no longer a threatened danger but current reality.
T'Challa has found them out.
What exactly is going on here? The Wakandan side is pretty simple: It is illegal to sell Wakandan technology without the approval of the Monarch, in this case T'Challa. The Atlantean side is a little bit more complicated. Technically the illegal purchase was authorized by Namor. The Submariner has given a vague command about doing everything to defend Atlantis. 'Everything' is open to a lot of interpretation - including illegal activities.
Going back to the action, some of the Atlanteans are captured by the Wakandans but some of them flee back to their undersea territories. The Black Panther pursues them. Soon T'Challa begins to realize what he is up against.
The Black Panther's approach does not go undetected. A chamber filled with air is provided for him to meet with Namor.
I'm calling this right now. T'Challa is a level-headed leader who can be trusted to negotiate. Namor, on the other hand, is Marvel's original hothead. Submariner and diplomacy simply don't mix.
Here's the crux of the argument.
So basically it's sovereignity. Who's system of laws will be used to judge the guilty parties? Before any more discussion, can be made, and as predicted, Prince Namor has once again blown his top. What was once negotiation has now become a tussle.
Although the fight is inconclusive the Black Panther is the underdog here by virtue of his fighting Namor in the Submariner's home ground.
As he moves through the undersea kingdom, the Black Panther manages to wake up someone who has been recuperating in Atlantis.
Thankfully the Hulk isn't siding with anybody here. He just wants to get out. And to the Hulk, that means the simple expedient of smashing a wall
Black Panther will be picked up by a Wakandan undersea team.
The Hulk will be pulled back in by the Submariner only to once again try to escape. The Hulk is so powerful he leaps clear to the surface.
Unfortunately, the projectile-like Hulk is mistaken for an Atlantean missile by the Wakandans who then launch a counterstrike. This all done without T'Challa's knowledge since the Black Panther was out cold at the time. His backup team made this decision. All T'Challa can do now is warn Namor that there is a missile headed towards Atlantis.
Namor redirects the missile with his awesome power.
It can safely be said that although war between Atlantis and Wakanda has been averted, the relationship between the two nations and their monarchs are now anything but friendly.