That is the new and excellent book by Philip Mansel and the subtitle is Splendour and Catastrophe on the Mediterranean, excerpt:
The Beirut dilemma goes to the heart of the Levant. At certain times — Smyrna in the nineteenth century, Alexandria and Beirut for periods of the twentieth — Levantine cities could find the elixir of coexistence, putting deals before ideals, the needs of the city before the demands of nationalism. Like all cities, however, Levantine cities needed an armed force for protection. This could be provided by the Ottoman, British or French armies, but not by the cities’ own citizens, since they were unwilling to shoot co-religionists. No Levantine city produced an effective police force or national guard of its own. The very qualities that gave these cities their energy — freedom and diversity — also threatened their existence. No army, no city.