We've spoken of borderlands, and how they are both linked and divided. Here is a border sea, differing in many ways but sharing the basic characteristic of the borderland. Proximity separates as much as it divides. It facilitates trade, but also war. For Europe this is another frontier both familiar and profoundly alien.
Islam invaded Europe twice from the Mediterranean — first in Iberia, the second time in southeastern Europe, as well as nibbling at Sicily and elsewhere. Christianity invaded Islam multiple times, the first time in the Crusades and in the battle to expel the Muslims from Iberia. Then it forced the Turks back from central Europe. The Christians finally crossed the Mediterranean in the 19th century, taking control of large parts of North Africa. Each of these two religions wanted to dominate the other. Each seemed close to its goal. Neither was successful. What remains true is that Islam and Christianity were obsessed with each other from the first encounter. Like Rome and Egypt they traded with each other and made war on each other.
Migration, Multiculturalism and Ghettoization
Multiculturalism and the entire immigrant enterprise faced another challenge. Europe was crowded. Unlike the United States, it didn't have the room to incorporate millions of immigrants — certainly not on a permanent basis. Even with population numbers slowly declining, the increase in population, particularly in the more populous countries, was difficult to manage. The doctrine of multiculturalism naturally encouraged a degree of separatism. Culture implies a desire to live with your own people. Given the economic status of immigrants the world over, the inevitable exclusion that is perhaps unintentionally incorporated in multiculturalism and the desire of like to live with like, the Muslims found themselves living in extraordinarily crowded and squalid conditions. All around Paris there are high-rise apartment buildings housing and separating Muslims from the French, who live elsewhere.