I have an idea to add clans. Each clan can get one clan dominium and flag. To destroy clan you have to destroy clan members dominions and then clan dominion. Being in a clan gives you bonuses, but when someone will destroy your clan you will have anti-bonuses. Creating of the clan can cost something like 100 hides, 100 iron, 1000 stone, 1000 wood and 30 boulders, that will create clan dominion obelisk.