America has always been a nation of immigrants and, whilst each wave has had an impact on Amercian culture, I personally believe that most have embraced the constitution and its values and been a net positive to US society. I expect any future immigrants to work out much the same irrespective of their original country of origin.
That's a bit of myth. For the first 100 years or so it was mostly Puritans from Great Britain. Then the Germans came later and the other European nations. Then the Chinese, Japanese, Mexican etc came a bit later in the last century.
Basically for most of it's history it has been a dual racial culture. About 90% Anglo-Saxon and 10% black and blacks from a very specific part of Africa.
There was a policy of integration up until not too long ago and they did embrace US values. Unfortunately multiculturalism has taken over and the idea that multiculturalism is bad has been deemed racist of xenophobic by political correctness so there's less integration and adoption.
The other main reason is simply the financial reason. Poor people want to take as much of the state as possible.
However that's not the American way for good or bad.