The M factor in American life is that we move a great deal. Andrew Cherlin thinks that this much movement may contribute to why our marriages and cohabitations break up so much. He cites Robert Baller and Kelly Richardson’s county-level data showing a strong correlation between moving, divorce, and suicide. I agree with Cherlin's view that American internal migration reflects more a search for economic opportunity than a general cultural "restlessness."
Americans move more than Europeans do, pulling up roots and starting anew. We don't think of moving from state to state as "migration," since it is all done within the U.S. The United States is so much larger than any European country, though, that even if they had the same level of internal migration that we do, it would disrupt their families less.
A few years ago I had in my family class a German woman who was in Kentucky as an au pair for an American family. At the end of the term I asked her to compare German and American families. One striking thing that she had noticed was that in both places, people she knew reported that their cousins lived far away; however, in Germany "far away" was an hour's drive, while in the U.S. "far away" meant an eight-hour drive.