Yet international migrants' total share of world population has been relatively constant at 2 to 3 per cent for decades

From Entrance Strategies a review by Eric Kaufmann of a couple of books dealing with culture and emigration. From the December 2013/January 2014 edition of the Literary Review.

The cultural cords - language or religion, for instance - that bind people together over time and place are selected by each generation. The symbolic menu is potentially infinite. Yet choices are constrained by the dishes chosen by previous generations. It would take a hard, multigenerational slog for an elite to convince British people to adopt Taosim or the German language as symbols of their national identity - it's much easier to stick with Christianity and English. Immigration of enough determined German Taoists, though, especially if they were resistant to English charms, could bring change. It's happened before. As Eugene Kulischer has shown, in AD 900 Berlin had no Germans, Moscow no Russians, Budapest no Hungarians, Madrid was Moorish and Constantinople had few Turks. More recently, Israel, Lebanon and Kosovo furnish examples of how migration can drive political change.

The collision between immigration and national identity is defining our epoch. This will only accelerate in the decades to come. The developing world produces 97 per cent of world population growth and is in the early stages of its demographic transition. The rich world is ageing and declining in native population. The demographic difference will peak in 2050 as economies converge: poverty and excess births in one region; wealth and birth dearth in another. Economic theory would suggest population should flow from the poor tropics to the temperate zones. Yet international migrants' total share of world population has been relatively constant at 2 to 3 per cent for decades.