An idea:
1. Create a world map (main land for the strong clans and many isles for the weak clans).
2. Randomly distribute the clans into the world map. Each clan has a territory.
3. The clan win the war can claim the territory of the failed clan.
4. A clan can only attack the clan connect to its territory.
5. Every season (e.g., 3 months) reset the world.

