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.
https://newenglishreview.org/Emmet_Scott/The_Fate_of_the_Roman_Cities_of_the_Near_East_and_North_Africa/