That's our Realm vs Realm system. When you first make your character you get to pick which nation: Pirate, Spain, Britain, or French. Then you try to generate unrest near conquerable ports by sinking NPC's of that nation outside of port and by also sinking players of the nation. You can reduce unrest by doing the same thing as the defending nation. You can also drop bundles which generate/degenerate unrest.
Then, if the port is at 10000 conquest points the port is flipped. The map is randomized out of 8 different maps. The port battle (see first post) decides whether the defender or the attacker gets the port by a 24v24 maximum and invites being sent by personal contention points. Personal contention points are points that you gain from generating unrest at that specific port. The points are sent to zero and then you can get more unrest by doing it again and you get special bonuses. For example extra doors to exit from in the Port Battle, stronger fortresses... etc etc...
If attackers get the port then they get points for that port plus port capture points, and this goes on until a nation gets 300 points and keeps it during the designated map check every week.
That's pretty much the gist of RvR.
Here's an example of a Port Battle Map.
