Once upon a time, the worlds people were governed only by local kingdoms at their most organised. Then came a european invention - the nation state - a political paradigm shift. And the world then had a stark choice as a consequence of the invention of the Nationstate:
Form a nation state or be ruled by another nation state. And that swept the world.
Then again, Europe did it again with the EU - a sort of supranational republic without any direct historic comparison.
And again the big political movement in the world is to either be ruled by a suprnational block. or join one. The EU is an example, ASEAN, and south america's Mercosur have replicated the EU model. Meanwhile nations states which did not join are left sitting by the fax machine, knowing that they must comply with whatever trade laws the big players pass, and to do so without a negotiation option.
Perhaps britain could chart an alternative path, but that would be extremely radical and strange.