You know that kind of makes Spock's the supernova threatened the galaxy thing more plausible seeing as taking out that much of the Federation and Romulan Empire probably would screw up a good chunk of the galaxy, especially if the Klingons decided to take advantage of the situation.
Oh, not even close. Here's Star Charts
' map of the whole galaxy:
See that tiny black dot in the middle of the white circle? The one labeled "UFP"? The whole of Federation, Romulan, and Klingon space combined are just a little bit bigger than that black dot. That's not a good chunk of the galaxy. It's not even a good chunk of the Orion Arm. To use an analogy I made in another thread a couple of years back, if the Orion Arm corresponded to Florida, the Federation and all its neighbors put together would correspond to Orlando and its suburbs. And size-wise, the Orion Arm is roughly as small a percentage of the galaxy as Florida is of the United States (including Alaska and Hawaii). Or maybe even less.