That's the definition of national culture but really if you're talking about the intangible "What is culture ?" question... it is probably more related to tribal behaviours that are more closely imprinted on our biology.
National culture is a subversion and an attempt to direct those tribal impulses towards people who share our citizenship.
You can't survive against adversity as a nation-state without a shared sense of values, culture and beliefs. That doesn't mean everyone is the same, just that, for want of a better term, they have certain higher level beliefs in common. Subversion? I don't know. We're all tribal, and if you want to call it 'subversion' to want to draw everyone within a national boundary into that same general higher level mindset then okay.
Jonathan Haidt, in a talk I've posted before, talked about this a lot, and mentioned the strange emotional feeling people get, including him, a liberal, when previous outsiders embrace these higher level beliefs. He specifically referenced the Khan family, the father and mother of Captain Khan who died in the US military. You'll remember him as talking about the American consittution and holding a copy in the air as he harrangued Trump at the DMC. They're born Pakistani and are Muslims. Haidt actually chokes up when he talks about that. And when he talks about a similar situation in the UK (the talk was in the UK) of immigrants showing loyalty and dedication to the royal family he still chokes up.
So yes, there is a powerful sense of common bonding with people who share our sense of national identity, call it what you will. And in the abscence of that sense of common bonding we get resentment, anger, and violence.