The Great Upheaval. That's what they called it. There were over fifty factions in Sigil until then. She decreed that only fifteen would remain after two weeks, and it happened. It didn't stop the bloodshed though. In that single night over ten thousand died. The remaining factions vied for believers, for belief is tangible in the planes. It is raw power to control the minds of those who follow your way.
On the Prime Material Plane it is the the year 1359DR. It has been 619 years since the Lady of Pain removed the majority of the factions from Sigil. In that time the Harmoniom and Xaotisects have been founded, and begun operating in Sigil. Recently, the Untheric Pantheon has been destroyed by Hoar, and the Unther Empire has devolved into chaos. There are rumors of the Gods becoming mortal, and roaming the planes for safety, while others are hunted on the Prime Material.
Many of the chaotic factions
You have come to Sigil, or perhaps you were born to an unlucky cager. The question that begs an answer: What will you do with your life? Perhaps you will join one of the factions, or maybe one of the guilds, or perhaps you've already become known as a factioner. Perhaps you'll search for planar doors, or go on travels to the Prime. Perhaps you prefer to be a seller of goods, or magic services. Anything is possible when traveling the Planes.