this is by no means the only way to look at nationalism, but one way you could look at it is as a battle between two predominant schools: either nations are primordial (they exist before nationalism) or they are modern (they come after nationalism, which itself came after roughly the industrial revolution). within nationalists, they either argue that nations are inherent and primordial in humankind in some way, or that nations only become a necessity after societal transformations that came after the industrial revolution. they're two opposing schools but keep in mind they agree that nations really do exist. now:
i'd recommend starting with anthony d. smith's nationalism: theory, ideology, history . anthony d. smith is a primordialist but he gives a decent overview into both fields. i havent read the whole book but a lot of it is really interesting and honestly not that hard to read. the point of this is to get a working definition of what nationalism even is
then there's benedict anderson who's a modernist whose main idea was that nations are imagined communities. his book imagined communities is a pain to read cuz the language is complicated but skim through a chapter or two. i had to read him first actually and that main idea is the thing you need to sorta get an idea of. its sorta important cuz its not from d. smith's primordialist perspective.
from there there's a guy called ozrikimli who wrote a book called theories of nationalism that goes over a bunch of nationalists, both primordial and modernist and otherwise, and what their theories mean. go over that and then see which guy in that you're interested in. this will give you a better overview of how other people have tried to define and discuss nationalism, and give you some names you can start pursuing from there.
unfortumately a lot of this stuff is at least a bit eurocentric so it may not align with the reality you're familiar with in china but it should provide a foundation to start understanding not just what nationalism is but how people interpret it, which ideally helps you understand how to write that earlier scenario.