Historians have a source problem. In order to talk about the past, we need sources. Anything else is just fiction. But the available sources are not neutral, evenly distributed, or representative. Sources that exist had enough going for them that they were created in the first place, and then available sources are the selection of all created sources which have survived the many possibilities for destruction over time. The first clause favors the creation of sources from the viewpoints of those who have power, wealth, leisure, and sufficient education. The second clause favors the preservation of sources which are continuously in use, well treasured, or buried in Egyptian sand. Both of these limitations affect pre-modern history more forcefully than modern: literacy rates were lower, so fewer people were able to preserve their viewpoints, and the acid of time has eaten away more of what was written. But even sources for modern history only represent the powerful enough and literate enough classes, and some modern sources still disappear before they can be copied.
The result is that dominant classes produce a disproportionate weight of source material. This is why, despite the fact that men and women have made up nearly equal proportions of almost all human populations, the vast majority of pre-modern sources were written by men (and were usually primarily about men). The majority of pre-modern sources were written by the ruling class (or by members of the educated class who wished to be ruling) or even more narrowly by government employees, and again, almost always about the ruling class or the state. The upper crust has never evinced much curiosity about how the rest live, and for much of human history the rest have been too busy trying to live to be able to preserve very much of anything in writing. The result is that, until the middle of the 20th century, almost all history being written was the history of the rulers. Since the mid-20th century, the mystery of the rest of the population has intrigued historians who have attempted to answer questions about the lives of women, children, farmers and other workers, slaves, ethno-religious minorities (such as European Jews), social deviants, and various other groups which are under-represented in the source materials which survive. History is the history of the society, not merely of those segments with the power to create and preserve source materials.
What does any of this have to do with non-Muslims in the Middle East?
Sources written by and for non-Muslims open up to historians viewpoints which are under-represented in Middle Eastern history. Almost all the widely known sources in Middle Eastern history, before the 19th C, were written by the ʿulamaʾ, the Islamic religious class who were experts in questions of religion and also almost always in the employment of the state (or wishing to be). They were useful to the state because they were literate (and state records require literacy, as do diplomatic correspondences) and because they could justify the state’s legitimacy to the ruled. But just like the preponderance of Medieval European sources being written by clergy, this shared religious class shapes the nature of the source materials. These ʿulamaʾ had very little interest in non-Muslims except when they got in the way (and thus the ʿulamaʾ wrote polemical treatises about how Muslim rulers should not employ non-Muslims, which only a few Muslim rulers in fact agreed with). Thus the “mainstream” sources in Middle Eastern history present a falsely unified picture of a dominantly Muslim society.
This mirage of cultural unity has not been interrogated by Middle Eastern historians, but in the magisterial work of Marshall Hodgson has been canonized as the “reality” of the medieval Middle East. (His Venture of Islam is truly a magnificent accomplishment, and half a century later is still a touchstone for so much scholarship, and he outdid most of his heirs in putting the Middle East in the context of world history. It’s just the assertion that the medieval Islamic world was “culturally unified” from Morocco to Indonesia is not only false; it’s preposterous.)
In medieval Europe, historians can turn to the Jewish sources and increasing numbers of vernacular sources to act as a check on the clerical sources, in order to attempt to counter-balance any clerical balance. Still, this is very difficult for the early and high Middle Ages.
In the Middle East, highly literate non-Muslim elites produced reams of sources ranging from the Cairo Geniza to the world chronicles of Bar ʿEbroyo, and they usually did so without large amounts of government patronage (often in a language which the government could not read, providing broader freedom of expression). These sources allow us to verify and check the court histories produced to flatter the rulers or the confessional bias of too narrowly religious histories. They are thus an invaluable resource for triangulating the past relative to the dominant religious discourse. Yet they remain under-studied, often considered the domain only of sectarian scholars and odd ducks who don’t deal with “mainstream” Middle Eastern history. But sources by non-Muslims, written in whatever language, are as much about the history of Middle Eastern society as any source from the ʿulamaʾ, and they provide perspectives which cannot be found among sources written by the ʿulamaʾ.
While the modern period provides a broader range of non-elite sources by Muslims, thus making non-Muslim sources less distinctive for the purpose of counter-balancing ʿulamaʾ sources, even in the modern period non-Muslim sources serve a distinctive function. As non-Muslims became a demographic minority, they often (though not always) experienced greater isolation from the resources of the state and what services it offered. Nevertheless, non-Muslims in the Middle East were frequently disproportionately literate, relative to Muslims with similar financial means and access to the government. Due to this greater downward penetration of literacy, non-Muslim sources can reveal a broader range of what was going on among the lower ranks of Middle Eastern society, and non-Muslims can act as a “canary in a coal mine” to reveal all sorts of phenomena which would be otherwise invisible to historians. Thus non-Muslim sources are especially valuable to Middle Eastern sources for providing a non-governmental perspective, and in modern times even a “view from below.”