That's right, nationalism can't exist in the USA because it's a country of European migrants.
Nationalism exists in the US but it is not the same concept as you and I know. The immigrants are also from everywhere not just from Europe.
It's a pity but I don't have personal experience, I mostly hear things from my friends and relatives who live abroad because I know them at some degree, we grew up in the same environment, I know their mindset, and their experience feels more close to my potential experience. I've heard from them that in the USA, after spending a few years, you do not feel like a foreigner, people in the USA make you feel like an American when you spend a few year with them.
I hear from many local people, who are in the USA that it's really a land of opportunity. Why do you think that it's a lie?
Because of many reasons but the shortest thing I can tell you is that 99% of the population is going through hardship, many of them living hand to mouth and are up to their necks in debt while 1% of the population holds all the money. In other words the "opportunity" belonged to a very small minority.
That's the most interesting part. By the way, in my country working class is very hardworking. Me for example, I work 12 hours a day because I want to live a normal life, I have a job and then I do freelance to pay a rent, to eat healthy, to go to the gym. I sometimes wonder, how good will my life be with my work ethic in the USA? Life is terrible and interesting at the same time. Sometimes I want to give up because working 12 hours every day for years to earn $1500 a month in my country, where the average salary is $500, kills me mentally, I'm tired.