An interstellar political body that established a hegemony over the civilized worlds and defeated the Independent Faction. Apparently formed of the merger of the U.S. and China. (The script for Serenity states the IAV Dortmunder was emblazoned with the "flag of the Anglo Sino Alliance.")
In the episode "Ariel" the Alliance officer arresting Simon, River and Jayne declared that he did so in the name of and by authority of "The Union of Allied Planets." Possible the Anglo Sino Alliance was the combined operation of migration from Earth-That-Was?