KI has already given a response to this suggestion years ago: they do not plan to bring any clan system to the game as it would lose its family-friendly environment. I've seen so many clans in my wizarding career to know why it would be a bad idea to create a clan/guild system: everyone will be hostile to one another, there will be plenty of profanity and colorful descriptions of fighting during "wars", and it would encourage players to create clans for the purpose of attacking people of specific demographic groups.
I think we are better off having clans/guilds formed in Central. It's safer, easier to organize, and the forum rules keep the conflicts and bad behavior under control.

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