VIENNA — Solidarity is essential to democratic societies; otherwise, they fall apart. They cannot function beyond a certain level of mutual distrust or a sense on the part of some members that other members have abandoned them. This is closely linked to a diminishing sense of common identity.
It is no accident, for example, that Europe's most successful welfare states were created in ethnically homogeneous Scandinavia. People in those countries had the sense that they could understand their neighbors and fellow citizens, and that they shared a close link with them.
The challenge nowadays is to maintain that sense of intense solidarity amid diversifying populations. There are two ways to do this: