Nationalism is blind identification with arbitrary borders.
To quote RAW: "“Most mammals mark their territories with excretions. Domesticated primates mark their territories with ink excretions on paper.”
And another famous quote that I got no idea where or who it's from but I totally agree, "think globally, act locally".
I do like the concept of a semi-permeable community, of acting locally, and I think locally-based decisions for the daily workings of a community are great, working for this local development, but certainly not at the expense of other places.
I always find absurd how people identify so much with arbitrary borders that the people who come from outside ("illegal immigrants, for example), are treated like a lesser human being, human rights dont matter anymore, they can suffer and it's all justifiable. We're all humans, with the same value, wherever we are from.
I was born in a country, live in another for some years, and while of course both places have influenced who I am, I dont care for nationalism, I consider myself a citizen of the world, unfortunately with limited rights to move around the world due to a specific paper document I have that says where im from.
Travelling around the world made me see how we are all so different and yet the same, how there's good and bad people everywhere (or, how we're all good and bad inside), and how each place has it's uniqueness and could be appreciated depending on your preferences.
And no, I would never go to war "for my country", because its not for the country, it's going to war for the interest of a few people in power, the poor people stay poor either way. Plus I dont believe in war ever being beneficial. Self defense if your country/neighborhood/house is attacked and your family/loved ones are in danger is very different, though.