Am I qualified to answer? I was born a dual Irish and American citizen, but I grew up in Ireland until I was 15 and then immigrated to the states. Going to high school here forced me to make friends among the Americans, there was no other community to be a part of. I also came to a small farming and lumber town, so there wasn't any other immigrant community to be a part of.
Now that I live in Chicago, I find that many of my friends are among the immigrant and ex-pat community. It keeps the homesickness at bay, and I sometimes need the culture fix. Not just music and dance and food, but people who understand my cultural references, have watched the same programmes and been to the same places. There is a strong Irish-American community as well, but I avoid them because they irritate me. But many of my friends are also Americans, whose families have been here many years.