You've lost me. Group identity is inherently cultural because it's a cultural meme, but group identities can be based on whatever ingenious humans can dream up. Probably the most recently-arisen sort of group identity is consumer-based - we consume video games, so we're "gamers." Religion has been tied to identity in the West as well. But once again, nation is something different. Nation is a product of the French revolution, it literally means "birth" in French, and I'd argue it was at least partially a product of the declining influence of the concept of Christendom. Like FP said arguing something is compatible with nationalism is very different from arguing it is nationalist. Bingo. Of course, it's somewhat more complicated than that and I think it'd be a mistake to suggest that most people living in, say, pre-Roman Gaul didn't have a basic awareness of commonalities with the people of neighboring tribes. But the tribe was by far the most important identifier.