^See, I don't think it's plausible that a single civilization could ever spread across that much of the galaxy. Again, it's a matter of sheer numbers. A single central organizing principle, whether a government or a defining national/cultural identity, can only encompass so many entities before it gets spread too thin. Any given part of the whole will only be practically able to communicate or interact with a finite number of other parts, so the wider it spreads, the less the entities on its outskirts will be connected to one another and the more they'll drift apart. The Federation could only grow to a certain size before the constituent subcultures on its fringes evolved different definitions of what the Federation was, or developed a sense of identity separate from other parts of the Federation. So eventually they'd schism into distinct political and social entities. It's inevitable. When we're talking about hundreds of millions or billions of worlds, there's just no way a single civilization could encompass any significant percentage of the whole. Maybe the UFP can establish friendly relations with like-minded neighbors who have friendly relations with like-minded neighbors and so on and so on, forming a chain of connections from one end of the galaxy to another, but beyond a certain point that chain would stretch so far that the civilizations at opposite ends of it would have effectively no contact at all.