Not sure I agree. China did by the Qin Dynasty. They have spent centuries defining the notion of centralized government right down to civil service exams (imperial examination system) for a thousand years. Rome was a pretty well-defined system of government, no?
I suspect the China issue was a carve out in the comment you replied too. Since they were referring to the west.
As for Rome, it was never a Nation in the modern sense. It started as a city state and became an empire.
My understanding is that nation states (where the rule and the border were defined nationality of the population) were born as a reaction against empire. Starting with the French Revolution, where the desire for the French to be ruled by French in France was new concept.
