Clans are one of the more fun aspects of the game; they allow you to have wars against other clans.
Clans may have up to 10 members, but they can have as few as just 1 member (the leader). It costs 10 gold bars to create a clan, and you must be at least level 40. There is no level requirement to join a clan.
Wars are similar to bounties because once you are in a war, it is a fight to the death. Normally when you battle someone and they are under 25% of their health, you will not be able to attack them. In a war you can be attacked at all times, and even if you only have 1 health point left, you may be attacked and killed.
When a war is declared against another clan, it must be accepted within 2 hours or the declaration will expire. The war will start one hour after the declaration of war is accepted. The war ends 24 hours after it has begun or until the war has been won.
Keep in mind that while you are in a war against another clan, winning attacks against lower level players will not be worth as much as a winning attack against a higher level player.