It is not PRC propaganda. It's the other way round: PRC propaganda exploits this national feeling.
I wonder how much of that unity sentiment is/was constructed and pushed on by leadership due to the area around current China being littered with competing kingdoms and a lot of internal strife and disarray throughout its history, not just the past 100 years.
In Chinese cinema, or at least some films, the theme of unity and to some extent 'glorious leadership' seems to be prevalent. Just came to mind that even in some Jet Li films (or equivalent) set in more ancient times you could probably be faced with some monologues or statements to that tune and at least I was a bit taken aback by how blatant it felt.
It's trying to push a narrative to argue what is part of the country...
Almost everything we appear to hold so dear and immutable or self evident seems kinda arbitrary depending on how far back you go and whether you consider yourself part of this team or that.
Nationalism or tribalism is a whole lot of make believe, is what I'm saying.