The Expansionists, also known as Bullies and Growers, were a Faction in Sigil over a thousand years ago. They believed that it was the purpose of all things to expand and grow in strength, power, and knowledge.
Their factol, Vartus Timlin attempted to take over the city. The end of that is well-known: Timlin was mazed and his faction dissolved. The middle is not so well-known: the twelve factols of that long-ago time met together in an underground inn (called the Twelve Factols in their honor even today) to beg the Lady of Pain to do something about the Expansionists and their power. Though Her Serenity does not normally take requests, that time she did.
Recently, however, Timlin has returned.
Well of Worlds
In the Cage: A Guide to Sigil