On nationalism edit
Nationalist POV-pushing, either for a group or against one, is a perennial issue on Wikipedia. However, it's important to acknowledge that such behaviour is not actually the result of any stereotyped national characteristic. Some people are simply dicks and such behavioural traits have nothing to do with nationality and everything to do with personality. That sometimes personality defects manifest as a wrong-headed perception of one's own nationality or that of others is simply a reflection of an inability to recognise personal prejudice. Changing someone's fundamental beliefs is beyond anything Wikipedia can hope to do, so instead we must try to manage the resulting behaviours. Bias ("if I can advocate X, I will") is a normal human trait; we all have it, and the better editors try to recognise their biases and either work around them or avoid working in areas where they may become an issue. Prejudice on the other hand ("I will advocate X, no matter what") is utterly unacceptable, and editors that demonstrate this trait must be shown the door.
On achieving NPOV edit
Imagine that you intend to paint your house green. Now imagine that you have only tins of blue and yellow paint to give to the painters. The ideal solution might be for the painters to mix the tins before setting brush to wall; the house will end up a nice even shade of green. A less ideal, but perhaps still workable, solution might be for the painters to cooperate in applying their separate colours simultaneously; the end result may not be perfect but should appear fairly even. If, however, the painters each try to overpaint the other's work - one wanting the house to be blue and the other yellow, the result will be a horrible mess of blue and yellow and every shade in between.