Nationalism and its evil twin patriotism are not the wonderful virtues as some people think. Nationalism at its heart is self love and xenophobia.
Nationalism comes in many forms and has many cousins. There is German nationalism, nationalism of countries that never existed, nationalism of countries that are not even homogenous. There is nationalism's cousins: racist chauvinism, both black and white, gender chauvinism, both female and male, religious chauvinism, and every sort of chauvinism you can think of.
It seems to start with someone identifying a group, assigning it to a rank in an hierarchy: themselves at the top, everyone else beneath. If we are all intrinsically equal, then patriotism is nonsense. Humans vary according to superficial details, like the food they eat, the cloth they wear, and the language they speak. Nationalists then proceed to heap more nonsense on top of nonsense. Nationalist start with the premise that wealth and military power are results of intrinsic superiority. This leads to the idea that the dominant class has superior food, a better language, and better looking people. The end result of this silliness is that there is a "Russian Mathematics" or a "Russian Chemistry" and that there is a "Russian Toothbrush." And the nationalists don't mean toothbrushes of a different color or weight, they believe that the teeth of Russians are better than the teeth of everyone else.
Based on these interesting assumptions and reasoning, the next step of patriotism is to exterminate all other forms of life. Nationalists want to try to put people like you and me out of our misery. This is done out of hat and a certain "racist compassion."
Wealth and military power are at best temporary and local. Even the Romans, the patriots they were, lasted only about 1,000 years, and their power was limited to the area around the Mediterranean. If you think your superior group will last forever in the age of widespread nuclear power, you are a cockroach. After the next big fight over the right to be called the Superior Man, only the cockroaches will be left to philosophize about the differences between Jews and Russians.
A Modest Proposal
I suspect my reasonable arguments will fall on deaf ears in the case of Nationalists (too deaf), and Patriots (think that it is a harmless peccadillo), so I have a modest proposal. We need a final solution. We must exterminate the nationalists; patriots, too! The nations of the world, through the UN, will round up the nationalists in cattle cars, send them to death camps located all over the world and, finally, we will be rid of American, Russian, Chinese, Dutch, British nationalists, white supremacists, black Islamic racists, and even those male, female, black, and white chauvinists. (If my list has omitted nationalists or chauvinists, it is only because the list is so long, not at all because I intended to play favorites.)
They will be burned alive, and their ashes will be used to plant a garden in the Cosmopolitan Park. There, someday when the last nationalist is gone, the few remaining citizens of the world will have a picnic and bring tacos, pita bread, borsch, pizza, coca cola, beer, and wine and be happy that the world isn't so monotonous in terms of people and boring when it comes to war and misery.