In Spain the Western Caliphate remained strong till the beginning of the eleventh century, then divided into numerous petty kingdoms, which continuously lost ground before the advance of the Christian states of the north till, finally, only the kingdom of Granada remained in the mountains of the south. Even this at last was conquered by the end of the fifteenth century, and the Peninsula came wholly under Christian rule.
In the Eastern Caliphate the Saracen rulers in the enervating lowlands of Bagdad exercised control over the very varied lands nominally under their rule only till about A.D. 800, when they were forced more and more to rely on mercenary bands of Turks to hold together lands continually in revolt. The temporal power passed naturally, then, from the hands of the Saracens to those of the Turks, and though it was not till the middle of the thirteenth century that the Saracen Caliphate at Bagdad was totally destroyed by the Mongols, yet the real control was exercised more and more by Turkish viceroys under different names, and independent Turkish powers were set up on the Iran plateau. Now we have seen that these Turks came originally from the plain. They were heathen : at most heterodox Christianity had been preached to them. Coming into contact with Mohammedanism they embraced that religion. Thus the destruction of the Saracen rule was no destruction of the Mohammedan power, rather an extension, for Asia Minor, which had never been Saracen, became gradually Turkish and Mohammedan, and the Turkish powers who descended into India set up more per manent Mohammedan states there than the Saracens had ever done. .
The Mohammedan lands of Northern Africa and Arabia, after the Mediterranean ceased to be a Roman lake, remained for long shut off from contact with Christian nations. They were not strong enough to extend temporal power across the Sahara, but the religion of Mohammed, the religion of the desert dweller, gradually spread from steppe to steppe and from oasis to oasis, till the natural difficulty of crossing the great barrier of the Sahara, increased by the presence of hostile tribes, was for Christian nations yet further augmented because these hostile tribes upheld a hostile religion.
The function of the Mediterranean has thus undergone a change. In early times it had been a barrier; later, it became under the Phoenicians a highway, and to the Greeks a defence. We find that the Romans made it a base for sea-power and subdued all the lands on its margin. With the weakening of Rome came a weaken ing of sea-power. The Barbary States and Spain became Saracen only because the naval power of the Eastern Empire was not strong enough to hold the whole sea, but neither was the Saracen able to gain supreme control. Thus the conditions were the same as in the earlier days of conflict between Rome and Carthage : the Mediterranean became a moat separating the rivals, though first one and then the other had somewhat more control. The islands became alternately Saracen and Christian. Crete and Sicily were held by the Saracens
for centuries before they were regained by a Christian power.
In the Persian Gulf and Indian Ocean new conditions arose. Here the Arab naval power had no competitor of any kind, and the extent of their earlier rule—stretch ing from the shores of the Atlantic by the Mediterranean, the Persian Gulf, and Red Sea and Indian Ocean to India, and holding the keys of the ways between East and West by sea and land—could not fail to induce the Arabs to become traders of a kind, so that Ceylon, though it never came under Saracen rule, was yet a centre of Arab trade in the eighth century.
The disruption of Saracen power, the division of the Caliphates and the practical independence of Arabia, Egypt and Barbary did not for a long time affect Arab trade. It was only when the Western Caliphate became weaker in the beginning of the eleventh century, that the new city states of Genoa, Pisa and Venice, which had risen on the ruins of the Empire, began to seize both the sea-trade and the naval power which till then had been in the hands of the Saracens. Their supremacy allowed of the dispatch by sea of expeditions of Chris tians on crusades to attack the Mohammedan power in Palestine itself when the rule of the Saracens was re placed by the more severe regime of the Turk. Even then, however, the Moors of Algiers and Morocco con tinued in some degree the control of the western Medi terranean, and retained it as corsairs and pirates for many centuries ; and more important still, there was, fpr an even longer time, no rival to Arab trade in the Indian Ocean, largely because there was a land barrier between east and west; indeed it is only in our own days that the destruction of that barrier has led to the collapse of Arab trade.
Thus we see the influence of the desert on history. The great belt of the Sahara and Arabia stretching into Asia and existing because of natural climatic conditions, has been and is the source and strength of Mohammed anism. An advance in the use of energy has taken place, because as a result of Saracen conquest the smile power had control of the Mediterranean and Indian Ocean, and the men of the West were familiarized with the ways to the East by sea as they had been with a way to the East by land when invasions took place from the plain : more energy became available. This result followed from the situation of the desert with reference to that of the diagonal water channel across the great land mass of Euro-Asia-Africa. Because the desert belt inter sected the channel, and because the land and not the water was continuous, the naval power belonged to the Arabs. Further, the desert reacted on the minds of men exposed to its influence during many ages, and through them has affected others not so exposed. These had all been stimulated to think, on a larger scale than had been possible previously, as to the reasons of things, and in turn the later developments of history were made possible.