I went to school in the north of the USA, then worked in the south of the USA. I have made many Mexican friends.
This is what I have learned from all this. Those who win a war, quickly forget about it, while those who lose the war, never forget about it.
I never knew about the American civil war until I moved from the north to the south of the USA. They don't teach this stuff in Venezuela. The northerner Americans never spoke about the civil war to me, or around me. The southerner Americans speak of, re-enact, sing of, re-live the civil war all the time and they are proud to be southerners.
I found that the Mexicans are the same way. All my Mexican friends did was talk about the Mexican/American war. I don't remember the last time I heard an American speak of this war. Mexicans learn about this in their Mexican schools and they learn to dislike the USA very much, even after they move to the USA.
It is hard for a Mexican immigrant to be proud to be a US resident, or for a naturalized Mexican to be proud to be an American. There are exceptions to the norm, but that's just what I've learned. The same isn't true for immigrants from other countries, Venezuela, Chile, Philippines, Cambodia, etc.