From a friend a question
What do you think of Nationalism in general?
good or bad?
helpful or harmful?
valuable or worthless?
And my answer
That is a multi sided question because there are two big questions hidden in the one. On one side is the recognition that you are living in many layers of a collective, from your neighborhood or church, to your city, your state and of course your country. In each of those cases you are a member more or less as an accident of where you live, but if you work with the other members to improve the situation in the collective, your life is improved because you get benefits from that collective, even when you might not see a one to one relationship in your benefits and effort.
There is of course the largest collective that is all humanity, and while 200 years ago what happened on the other side of the globe might have few consequences to you, that is certainly no longer the case, from your factory that got shipped to China, to the collapse of the Antarctic ice shelves. So while you indeed do want to improve each of your other collectives, and need to work on that as you can, you need to work on the global one as well. If Chinese workers got a decent wage you would have more jobs at better wages, If the Antarctic Ice melts I get waterfront property.
There is of course another very much darker side that lays underneath any recognition of one's collective that can go from simply annoying to the worst sort of mass murder and genocide. At the lightest it is properly called triumphalism, that your collective is the most desirable to be a member of because of aspects you like and achievements you are proud of, plus you are in it and others are not. Internally this can gin up the troops to make more sacrifices for the collective, and under wise leadership can still bring cohesion and a better outcome for the extra effort, but from that point forward the slope begins to get slippery.
Things begin to get dicey when a collective adopts strong triumphalism that is directed outwards, especially when your collective is one of two or more in a larger collective, your collective can generate annoyance to downright hostility. A leader of your collective, particularly if unimaginative, or merely has an agenda to benefit himself at the expense of the collective, can use the hostility generated to create more triumphalism and get more support and sacrifice, even beyond what might normally be willingly given. This can cause a cycle of hostility that can easily get out of hand.
At some point there gets to be the idea that the Collective would be much better off if other collectives were not a part of the larger collective, and by eliminating them eliminate the source of hostility. This might take the form of wanting to divide the land in half, one collective or the other to run away or be pushed away, or if there is no away then mass murder can start. By the time this Eliminationism is in full flower, getting cooler heads to shut it down can be difficult or impossible, and the greatest evils humans know can be commonplace.
The trick then is to be mindful of the triumphalism, and hold leaders carefully accountable if they gin it up beyond that lightest levels, but particularly if they are unworthy of that leadership they will strongly resist efforts to do so. There in lies the Bane of Humanity.
A good Reference: "Eliminationism in America": Parts I, II, III, IV, V, VI, VII, VIII, IX and X, and Appendix.