The US was always the melting pot model, where immigrants assimilated into the general American culture. The second generation spoke 'Merican just like the locals. Italians, Germans, Poles, all became standard USians.
And it continues to this very day. Your average latino American or Asian american just about can't assimilate quickly enough most of the time, and within one generation most fully identify as Americans without rejecting the fundamentals of their origin culture. One can wish and wash about racism in U.S. society in many ways but compared to many countries, the country is remarkably effective at assimilating people from extremely diverse places and making them feel like they belong to its society. Canada does a decent job of it too but I've never quite seem any country pull it off as well as the U.S., maybe because it has such a specifically charismatic cultural image from decades of overwhelmingly, globally popular cinema, pop culture and etc.