The human presence on the shores and in the islands of the Mediterranean has altered the environment; just as wastes have been created, new land has been brought under cultivation (a recent example is the Pontine Marshes in Italy). Environmental degradation already occurred in antiquity, and ecological historians have debated how far the Mediterranean was capable of adjusting to the impact of humans by a process of what might be called self-correction. Gains in one area may have compensated for losses in another: the granaries of Tunisia declined precipitately in the Middle Ages, but other sources of supply (such as Morocco) came into their own. In the modern Mediterranean, advanced technology makes it possible to dream of sophisticated agriculture using sea water or dry soils to produce basic crops — one thinks here of the achievements of agronomists in Israel. And yet the simple fundamental point stands: the Mediterranean has always been, and will have to remain, a zone in which shortages of some essential goods are compensated by exchange with regions better endowed with those goods.

The challenge now is to make that system work once again, for it has largely broken down. The countries on the northern shores of the Mediterranean look to Brussels (or maybe Berlin and Frankfurt) for a solution to their economic problems. They have turned their backs on the Mediterranean, and on their true vocation which lies there as much as, or more than, in Europe. Economic interdependence can, in the right conditions, have the capacity to reduce tensions — and, in the wrong conditions, to inflame them: an argument has been developing around the energy supplies to be found beneath the seabed off the Cypriot coast, the focus of competition between Turkey, Cyprus, Syria, Lebanon and Israel. 

There is another feature of the Mediterranean in past times that has to be emphasised, since it is less obvious in the 21st century.  The desire to obtain goods encouraged merchants to cross political and religious boundaries, particularly those between Christendom and Islam, but also boundaries within those religious spheres: between Sunni and Shia, between Catholic and Greek Orthodox. The Mediterranean has been a principal meeting-point for the three Abrahamic religions and interaction has been regular and even at times intense, even in the age of the Crusades. Religious cross-currents have included the spread of the Jewish diaspora into the Hellenistic and Roman worlds (notably Alexandria); the underground Christian movement and its transforming role in the later Roman Empire; the arrival of Islam and the conversion of the peoples of north Africa and parts of southern Europe to a dynamic new faith, while all the time the three religions (and, at earlier points, paganism) taught one another elements of theology, moral codes, even snatches of liturgical music. Singly and en masse, pilgrims moved back and forth across the surface of the Mediterranean. Aboard a medieval ship you might find Christian pilgrims bound for Jerusalem and Muslim ones bound for Mecca, who, despite mutual suspicion, knew that they were engaged in the same sort of spiritual enterprise.    

All this points to the importance of the theme of migration within and into the Mediterranean region: colonists from Greek and Phoenician cities heading westwards to Sicily (ninth century BC onwards); Germanic peoples settling in Spain, Italy and North Africa (third century AD onwards); Arabs from Yemen and Arabia, Berbers from the Maghrib, Copts from Egypt, settling in Muslim Spain (eighth century AD onwards); Crusaders, Venetians, Catalans . . . Yet in the 19th century and particularly the 20th we begin to see the reverse process on a massive scale, as Mediterranean peoples sought livelihoods in the New World or in northern Europe (with interesting cultural results such as the spread of pizza). One cannot, of course, ignore the effects of colonisation and then decolonisation, as large numbers of European settlers took up residence in 19th-century Algeria, Tunisia, Libya, and so on, only to depart in the second half of the 20th century, along with indigenous inhabitants, many of whom then settled on the northern shores of the Mediterranean, in and around Marseilles and Nice.