Perhaps one problem is the expectation that integration will go smoothly and quickly. The history of immigrants in America is one of multiple back-and-forth trips to the old country, many people who came went back, and long-term connections with relatives and cultures that span generations. People whose families came here from Italy or Ireland in the 1930s still visit their cousins "back home." They clearly identify with their traditional culture. My grandmother kept in touch with her relatives in England 100 years after the family had come over here.

It takes a LONG TIME for people to integrate. The New World has this expectation built in, but if anything the United States is probably better at it than other places like Canada and South America where the connections to England, France, Spain, and Portugal are still very strong. For a country without the expectation of immigration as part of it's culture, the process can be expected to take even longer. Like a hundred years or so.