ORIGIN AND DEVELOPMENT OF ISLAM 23 of the Nile valley and the great chasm of the Red Sea) and of the sandy belt which traverses Asia throuh central Persia and the Gobi desert. With the exception of the mountains and highlands, the land consists mainly of desert and sand-covered plains between the hills. Agriculture is scanty and sporadic, providing a subsistence to a limited number of people. It just could not have produced enough surplus for the flowering of a brilliant civilization. Within the Arab world, one can easily identify three zones that differ widely from each other in social structure and in political and economic organization: the Arab East which includes Syria (embracing the present-dav states of Syria, Lebanon, Jordan and Israel), and Iraq; the countries of the Nile which means Egypt and the Sudan; and the Arab West stretching from Libya to the Atlantic and including present-day states of Libya, Tunisia, Algeria, Morocco and Mauritania. Egypt alone in this group has always been, and still is, the peasant civilization although it may not have been feudal in the customary sense. South Arabian Civilisation On the peninsula itself, southern Arabia has its own distinct features. The division between south and north was a significant one: Joel Carmichael says in his book, The Shaping of the Arabs: The division may be rooted in the factual situation of the nomadism of the peoples of the north and the sedentary and agricultural condition of the south. This division was felt to be so strong indeed, that it served the fourteenth century Arab historian Ibn-Khaldun as the framework of his whole view of world history, which he conceived of as the result of the reciprocal interaction between the Bedouin and the city dwellers.3 In southern Arabia there were highly developed civilizations, Sabaean, Minaean^ and Qatabanian, based on agriculture and spice traffic; and trade with the outside world brought prosperity to its people more than a thousand years before Christ. The Arab kingdoms in the south dammed the water courses, built castles and temples, and developed agriculture to a remarkable degree. They pushed their trade centres far into the north.4 In historical times wave after wave of Arabs came up from southern and central Arabia and found their way into the settled lands of the fertile crescent, urged on by poverty and hunger. Settlements and oases can support only a limited rnimber of inhabitants; the pasturage of the steppes can feed only a limited number of camels and herds, and when that number is exceeded a war of conquest or annual raids on the settlements become the only alternatives to starvation. The great conquests of Islam of north-east and north-west countries with the help of the Bedouins of the desert represent a similar phenomenon of increasing pressure on the land resulting in mass migration towards the north. This had repeatedly happened in the history of the Arabs. Whenever some calamity afflicted the south, people migrated towards the north in search of livelihood. The breaking of the great dam of Ma'rib is one