Nationalism is an ideology responsible for more conflict, suffering, misery, and death than any other except perhaps religion (in that regard, the two can be considered forms of the same underlying problem). It continues to plague this planet and drive millions to slaughter, even though it fortunately doesn't do it any longer in the place where it originated, i.e. the continent where I was born.
Clearly, if we are to achieve maturity as intelligent beings, we need to get rid of it. We invented it, we created, we should be able to undo it and throw it into the dustbin of history.