Ignoring the massive cost, legal hurdles, and the opinion of the residents/government/outside powers, if you could magically grant independence to certain territories or form new bigger nations from existing ones with no repercussions to yourself, what new countries would you create?
Please treat this as a non-serious post, let’s not get into a massive political debate, those never end well.
(Apology accepted. Sorry if I was painfully American)
The (very British) definition of “nation” you used isn’t at all sensible with what the OP asked. To use meriam-Webster’s definition as a guide, you meant definition 1.a.1, but there are six other listed definitions.
https://www.merriam-webster.com/dictionary/nation
That being said, a “nationality’ (meaning the same thing you called a” nation") will inevitably arise within any soverign state (https://www.merriam-webster.com/dictionary/state, meaning 5.a) which persists for a long enough time. The most obvious example perhaps being my own country, in which a distinct “american” /nationality arose after our civil war, although the distnct non-British nationalities of “Canadian” and “Australian” in those respective countries would also be excellent examples. (As would “british” itself.)
While we’re on odd meanings of words, it’s probably worth mentioning that “race” is an archaic synonym for the same idea, although that usage fell out of common usage some time after the establishment of chattel slavery based on skin color.)