I had this idea a long time ago, but it was more thought out.
Across the sea in Port Town could be some sort of tropical pirate town, prefably a cave. They would have pirate ships that would come over the sea to attack Port Town, Port Town would then have to defend themselves. As the pirates ships attack different parts of Port Town the "town health" goes down. The bank would be the most vurnable spot, as that's the main point of the attack. The life of the pirates would be their ships. Pirates could leave the ship and steal cargo from the Port Town shop, giving them small cash profits and items for their home shops. Each faction could have people trained in repairing which would be able to give small amounts of health back to the town/ships. If the town health reaches zero the pirates win and they gain money from the bank, collected from deposit fees/fines/donations. The pirate town would gain money in a similar fashion, with a few tweaks. If the town defeats the pirates they get "booty" from the ship which may include exotic items and gold. The towns use the money they earn to increase their power with things such as cannons and better armor. There could be assigned commanding officers to help direct attacks(npc forces?) and special moves to boost their npcs/players with junk like attack/defense/speed boosts. To avoid constant raiding, they could be set up at certain times by the governing forces(Badspot?).
There's some more to it but that's what I remember off hand.