For decades the core of the debate raged around two opposing positions: One school of thought looked to climate change; another looked to human action. By the late 1940s however the evidence had moved decisively in favor of the latter, and the definitive work was published in 1951 by Rhoads Murphey, Professor Emeritus of History at Harvard. In an article entitled The Decline of North Africa since the Roman Occupation: Climatic or Human? he provides a detailed outline of the problem. I shall quote him at some length, as what he says is most instructive:

“The Romans were an agricultural people who expanded into their Mediterranean empire from a relatively humid base in Italy. It was natural that they should extend this approach to the natural environment into the African provinces. The Arabs were on the contrary a nomadic people, nurtured in the true desert of Arabia, and totally unused to an agricultural economy. Their technique was unequal to understanding or managing the highly-developed irrigation works of North Africa bequeathed to them by the Romans, and they had no need for dependence on the agriculture which these works had supported. Their different use of the land does not need to be explained by a change in climate. No military conquest is conducive to the maintenance of civil order nor the administration and technical organization which an intricate irrigation economy requires, especially when the conquerors are nomads. The Arab conquest destroyed the Roman irrigation works, or allowed them to deteriorate, and established in their stead a nomadic pastoral economy over most of North Africa.” (Rhoads Murphey, “The Decline of North Africa since the Roman Occupation: Climatic or Human?”, ANNALS, Association of American Geographers, Vol. XLI, no. 2, (June 1951)).

Murphey goes on to note that “Similar well-documented cases, for example, the Masai, are recorded from east and West Africa, where Hamitic or semi-Hamitic peoples in later ripples of the Islamic invasion displaced and overlaid sedentary Negro agriculturalists and substituted nomadic herding in areas where the only change was in social and economic custom rather than in the natural environment.” (Ibid., p. 124)

He continues:

“Nevertheless, it is possible that the changed land use which the Arabs brought with them did in time affect the natural environment in a critical way. By the end of the eighth century AD there were approximately one million Arabs in North Africa. Each Arab family kept a large flock of sheep and goats, variously estimated at between fifteen and fifty per family. Goats are notoriously close croppers, and their unrestricted grazing in the Mediterranean area has had a virtually irreparable effect. In North Africa too, the added presence of several million goats undoubtedly destroyed large areas of grass, scrub, and trees, increasing the run-off, decreasing precious supplies of groundwater and lowering the water table perhaps critically, adding to the erosion of water courses, and disrupting the optimum distribution of surface water…” (Ibid.)

Furthermore, “Contemporary Arab disrespect for trees (notorious in both Arabia and North Africa) except as lumber or firewood, and lack of understanding of the long-term value to themselves of tree-cover may suggest a further deteriorating effect of Arab land use on the productivity of North Africa. Indeed, one student of the problem, while agreeing that the North African climate has not changed significantly in the last 2000 years, states that the primary cause of the economic decline during that period has been deforestation, for which he lays the blame at the door of the Arabs.” (Ibid., pp. 124-5)

We should note that even those who continue to argue for a radical climate change in the seventh century are nevertheless compelled to admit the great destructiveness of the Arabs in the regions they conquered. The latter is revealed by excavation, and is fully supported by contemporary written accounts.

Yet even allowing for the destructiveness of the Arabs, and for their habitual misuse of agricultural land, this in itself does not explain the rapid and complete degradation of the cultivated territories of the Middle East and North Africa. After all, we must suppose that native husbandmen would not lightly have permitted incoming Arab nomads to graze their goats on carefully tilled and planted fields. Furthermore, the Middle East and North Africa had seen numerous invasions before, some of them very violent indeed, but none of them led to the complete destruction of the agriculture of the region. What was so different about the Arab Invasion?

In order to answer this question we need to consider the unique nature of Islam and in particular its application of political and social control through sharia law.

After the conquest of a territory and the submission of its inhabitants, the dictates of Islamic law, as enshrined in sharia, meant that the non-Muslim inhabitants could never again enjoy lasting peace and security. In theory, the “religions of the Book” (i.e. Christianity and Judaism), enjoyed a special “protected” (dhimmi) status under the new regime. In practice however the position of the Christian and Jewish populations was anything but protected. This was because under sharia the rights of Jews and Christians were subordinate to those of Muslims. The legal testimony of a Muslim always trumped that of a Christian or Jew, no matter how many Christians or Jews testified. In practical terms, this meant that a dhimmi Jew or Christian might be insulted, robbed, or even murdered in the street, without any hope of legal redress. If such a complaint were taken to the authorities, the Muslim culprit would claim that the infidel had insulted the Prophet or the Koran. Two other male Muslim witnesses were needed to substantiate this claim, but these were invariably forthcoming, and the suit ended in the execution of the Jewish or Christian complainant.

As might be imagined, such oppressive conditions meant that Christians and Jews lived in permanent fear of the predatory attentions of Muslim neighbors, with the result that, over the centuries, the pressure to convert to Islam, or to emigrate from the Muslim-controlled territory, became almost irresistible.

A further exacerbating factor was that under Islamic law Muslims have a right to subsist off the labors and property of the infidel. This is enshrined in the concept of jizya, the tax which all infidels living in the Dar al-Islam must pay to their Muslim masters. But it was not just the Caliph and his emirs who were entitled to live off the infidels. All Muslims, irrespective of position, had this right; and Islamic law thus sanctified the plundering by individual Muslims of the local Christian and Jewish populations.

The long-term consequences of such an outlook are not too difficult to imagine. A general climate of banditry and lawlessness was fostered; and we see, for example, in a very immediate way why immigrant Arab goat-herders in the Middle East and North Africa felt free to allow their flocks to graze on the cultivated lands of their Christian and Jewish neighbors, thus destroying the agricultural viability of these territories and reducing them, within a very short time, to arid semi-desert. One of the most immediate consequences was a dramatic decline in the population.

Although precise figures are unavailable, we know that the medieval populations of Anatolia, Syria, Egypt, and North Africa were much smaller than those under the last Byzantine administration. Estimates put the decline at anything from threefold to tenfold; and the result was that by the later Middle Ages large parts of the Middle East and North Africa comprised sparsely populated wasteland, housing economically oppressed and largely impoverished populations. In the fourteenth century, for example, the Islamic scholar Ibn Khaldun, writing in the squalor of what is now Tunisia, marveled at the wealth of a visiting delegation of Italian merchants. And the same attitudes continued to produce the same results well into the nineteenth and even twentieth centuries.