[Septimius Severus]

That is pretty much a given. No team is going to pay for an attack on the AI unless it benefits them (is in province they want to clear out or a province on their border to assist with expansion). Though under the rules, generally that province belongs/is the responsibility of the client to claim. Of course Zegc may be saying that any attack on an AI that is giving you problems is good, and there is some truth in that, though keeping the land is a bit different.

What is happening I suspect is that Atlantis is reaching their maximum expansion level under the rules (perhaps the motivation behind Zegc's offer). This was actually expected and planned. With 270 provinces we've got about 12-13 provinces per player. Zegc (actually doing suprisingly well) will probably top out at around 20 provinces (maybe more if Atlantis is willing to go into non-contigious areas to grab indies). At that point, the rules provide that Atlantis will be able to launch attacks to regain lost provinces thus maintaining a relatively stable number of provinces.

Keep in mind, Atlantis only needs enough provinces to give it a decent amount of gems and income to enable it to do it's job of serving the needs of the human teams. The mercs are not intended to be a major player in the game (in terms of grabbing up a large amount of provinces) and should have no ambitions towards winning. The Merc's don't align themselves with any specific team and have no alliegences except to gold.

The ability of Atlantis to survive in the long run (after the AI has been dealt with) will depend on the merc's ability to make itself useful enough to human players that they won't feel the need to wipe them off the face of the map for the VPs or territory they may control. Thus I don't want them to have a huge amount of territory or otherwise compete in a major way with the human teams.

Atlantis can gain some provinces above this threshold under the rules by retaining unclaimed provinces. I also suggested loansharking (defaulting on a loan in particular) as another possible method, but overall Atlantis is not meant to be an ubernation nor necessarily a permanent fixture of the game.