It's just an extension of society in general. I live in a neighbourhood, I am a member of the community. I am proud of my neighbourhood even though I am not dir

It's just an extension of society in general. I live in a neighbourhood, I am a member of the community. I am proud of my neighbourhood even though I am not directly responsible for everything positive within it. Same principle scales all the way up to countries. It's a way of bringing people together (see: national sports teams). Nationalism is, uh, not without its downsides. But the motivations are pretty clear.