If a clan attack a town, like Siege, then they can build catapult, well we all know that they destroy the wall, but if a clan leader fire those catapult and destroy the wall, then they also gonna pay for it, i mean build the wall up again, i think it could be very cool.
Also i think clans could build some trade stuff, in the towns, so people can get the goods and sell it in another town.
Sorry my bad english, but i hope all understand what i wrote