Aftermath of the Terran Civil War
By the time the dust settled in the Terran Civil War, the Rump and Rim Federations were not at all like the Federation itself had been before the war. The power of the Corporate Worlds had been conclusively broken by their responsibility for the war, and the Rim, of course, was just as anti-Corporate World as the Republic. By the time the Orion population was added to the population of the Rump (the Rim -- although technically part of the Rump -- did not join the Pansentient Union for Quite Some Time), the Croporate Worlder politicians discovered that they had suddenly enjoyed the same experience they'd planned for the Fringe Worlders: submergence and dilution of voting strength in the new, monster political entitty they'd created.
Of course, it would be a mistake to think of this as too total a fusion between the Khanate and the Terrans. It's really rather more like the relationship between the Khanate and the Empire of Gormus, although exactly which is the Khanate and which the Gorm following the changes wrought by the Civil War isn't quite as clear cut as one might have expected it to be.
As far as the Orion and the Fringers are concerned, the real concern of the Fringe was never anti-Orion chauvinism; that was the way it was portrayed by the Corporate Worlders and their PR machine, and it was so much of the "politically correct" humanocentric view of the universe (as purveyed by Heart World and Croporate World news media, academics, and political pundits) that even as astute a student of history as Ian Trevayne was at least partially taken in by it. The real reason for the Fringe's opposition to the amalgamation of the Khanate and Federation was precisely what Oscar Dieter told Taliaferro it would be: they'd done an analysis and recognized the cynical move to reapportion them out of the representation they'd finally earned for exactly what it was. The wartime propagandists of the Federation were quick to play up the traditional "hatred" of the Fringers for the Orions, but in fact, that "hatred" had a lot more in common with the late 20th century tradition of "hatred" between "Rebels" and "Damnyankees." It represented a holdover of a past tradition which was at least as much a matter for humor and jokes as for any genuine antipathy. As a matter of fact, the Fringers and the Tabbies pretty much shared the same view of the Corporate Worlders, and I suspect the Khan actually took a certain felineoid delight in pushing through the amalgamation and giving the coup de grace to the Corporate World's political dominance.