i disagree, germans also vehemently hated each other (in the wars in some regions half of the people got killed) and so did the scandis. these things can change, usually by creating a super-identity, and maintaining it for a long enough period of time. yugoslavia got cursed by two world wars and then communism with a cult of personality (thanks to the british). if they had managed to maintain a yugoslavian identity continuously for 2-3 generations it would have worked (it's basically what all the other european nations did)
Germany