John Berry, a Canadian researcher on acculturation of immigrants, gave a report to the World Congress on Positive Psychology that I am attending. He studied the different ways immigrant youth in Canada dealt with the tension between their old and new societies. He identified four ways this tension could be resolved.
The best way, for both the immigrants and the host society, is integration of the two cultures. Some immigrant groups encounter more discrimination, and are more inclined to keep their own culture, leading to separation. A few immigrants favor assimilation to the new society - mostly refugees who fled a bad situation in the old country. Most dangerous for both immigrants and natives is the marginalization of the immigrants, who feel no attachment to either their new or old culture.
The results for his survey of Canadian immigrant youth:
This seemed a very timely study to me in the light of the right-wing anti-immigrant terrorism in Norway that happened as the Congress is meeting. Berry reported that settler societies, such as Canada and the United States, promote integration of immigrants, which reduces tensions between the two groups. European nations, by contrast, fall into separation, or worse, which heightens tensions between the two groups - and sometimes leads to nativist terrorism against immigrants and those who welcome them.