To OP - have heard that line about nationalism being the cause of evil many times.  I think that happy families make better neighbours.

Countries who are able to control their own legislation and live in a way that suits them, expressing their own qualities and character, can better tolerate a neighbour who is different but happy in their own individuality.

Using the family analogy - most of us are happy to live within our wider family, having our say and giving leeway to each other, but would not be happy to live in a commune.