i'm using your exact definitions!!! you didn't have a quantitative threshold for it
is new york city allowed to secede? is each neighborhood in nyc allowed to secede? how many secessions can you have? are you in favor of a billion city states?
Fine. "An area with a culture and national identity distinct from the surrounding areas." Many Catalans identify as Catalans, not Spaniards; I would think most New Yorkers see themselves as Americans before New Yorkers.
Or, if you're going to continue being pedantic, how about 20 000 square kilometers?
Oh so what should qualify as an independent nation is based on your subjective, arbitrary idea of what you think a nation should be? Why does this even matter to you anyway? You want to federalize the EU, you should want less sovereign nations, not more.
I would never argue that nations should be forcibly federalized. If they don't want to participate, they don't have to.