(If Andy, or anyone else, would like to delete this post, feel free to do so.)
Four years ago, the Blood War spread to the Astral Plane, when a Pit Fiend suspected that agents of the Abyss had infiltrated Githyanki society. The forces of Baator, including many mortals bewitched into infernal service, invaded the Astral Plane and sacked the Githyanki capital, and brutally executed their loathsome Lich-Queen. The baatezu have declared that the Astral Plane will become a staging ground to spread order throughout the Transitive Planes and encircle the forces of Chaotic Evil. Repulsed at the occupation, and furious at the treatment of their most respected artifacts, Githyanki insurgents conduct hit-and-run tactics on the backs of red dragons.
The invasion--and the subsequent savagery and looting--upset deep fissures in Gith society. For generations the Githyanki had repressed and enslaved their near-kin the Githzerai. With the Lich-Queen's finally over, the Githzerai are rebelling, hoping that others of their kind--who had established sanctuary in the Ever-Changing Chaos of Limbo--will soon come to their aid.
Almost all of Gith culture in the Astral Plane is breaking down, either ruined by the Lich-Queen's inscrutable malice, the fury of the invasion, or the madness. T'anarii from the Abyss have come to sow chaos and mistrust, and ensnare the infernal Baatzu in an geopolitical (plano-political?) mess. Many disillusioned Gith, horrified at what's happened, believe this is all the machinations of their ancient foes the Illithids.
Play would alternate between three "parties" --
A group of Halfling soldiers just awakening from the geas that led them on this mission. They crew a lobster-shaped armored tank, an Apparatus of Kwalish. These characters don't speak the language, and are many, many planes from Sigil (or the Prime, whatever). The command structure of the coalition is complex, and includes a few Celestials who hope, somehow, to make Gith society more Good-aligned, even though the occupation also involves devils.
A group of Githyanki blackguards and dragon-riders, seeking to resurrect the Lich-Queen, expel the invaders, and establish a society more in keeping with the teachings of their Prophet, Gith.
A mixed-race family of Githyanki/Githzerai Commoners, who are caught in the middle of all this and must scrounge around for a means to survive, possibly escaping from the Citadel of the Lich-Queen and eventually making their way across the Astral for refuge somewhere else.
Each session involves one of these groups in reaction to whatever was just done by the other group in the previous session.
(I would apologize to the actual human beings involved in these tragic events if I knew anyone's name. As it is, insensitive dimwittery is the nearest I can come to grappling with a mind-boggling situation.)