Cosmo Babylonia, originally named Frontier IV, was the first colony to be attacked by the Crossbone Vanguard. It was then taken over, renamed, and became the capital of the Ronah family's new aristocratic nation.
A new nation established by the Crossbone Vanguard, made up of the captured space colonies of the Frontier Side. Under the leadership of the Ronah family, Cosmo Babylonia is dedicated to the principles of aristocracy and noblesse oblige. Cosmo Babylonia soon establishes an alliance with the Jupiter Fleet, allowing it to stave off Earth Federation interference with the threat of an energy embargo.
The Crossbone Vanguard continued to hold control over the Frontier colonies, until the return of Cecily Fairchild in U.C. 0125, who denounces Meitzer Ronah, resulting in a civil war between the Ronahs and their respective supporters and pro-Federation supporters. Due to the infighting and the added weight of repercussions demanded by the Earth Federation for taking the Frontier colonies, Cosmo Babylonia ultimately collapses in U.C. 0128, with the Federation retaking the Frontier colonies after the Ronah family went into bankruptcy.