What was the Islamic attitude towards and tolerance level of other religions, prior to the sacking of Constantinople by the crusaders and the destruction of Baghdad by the Mongols?

Why the West attained a period of dominance is a separate question that I won't address here, although I will point out: Latin Christians conquered Constantinople from Greek Christians in 1204. That doesn't seem to be a breaking point in Muslim attitudes towards the "Franks" and "Romans" for, well, obvious reasons. And as we'll see, it's dangerous to draw conclusions about what the situation and attitudes today might be from a range of attitudes in the past, because even interpretations of a sacred text depend heavily on the historical context of the interpreter.

It is impossible to speak of "the Muslim attitude" towards other religions and their practitioners in the early Middle Ages, just like it's impossible to identity a universal view in the modern world. Instead, we can look at a range of laws and literary portrayals from specific historical contexts, and see how particular events affected them.

The Quran's specific views on non-Muslims are fairly well known. Jews and Christians share an Abrahamic foundation and are dhimmis or People of the Book. They can be permitted to exercise their faith freely in Islamic territories while subject to restrictions such as an increased tax. Practitioners of other religions (the web of Middle Eastern paganisms, Zoroastrianism, etc) are not afforded that leeway. A famous medieval, though not authentic to the named ruler, example of restrictions on dhimmis is the Pact of Umar. While we can't know whether restrictions like this were ever officially deployed, it shows us what the relationship between Muslims and protected non-Muslims was idealized to be by at least one group of Muslim legal scholars.

In practice, the application of the Quranic principles here varied. Sometimes Zoroastrians were extended dhimmi protection, and sometimes Jews and Christians weren't. The Almoravid and Almohad dynasties in North Africa and Iberia, for example, attempted to force Jews in particular to convert to Islam. Their Umayyad predecessors in the west, on the other hand, actually discouraged conversion among the lower aristocracy, for the tax benefit.

The question of what jihad meant in early Islam is as vexed as it is today. There's no question that the infant religion's adherents achieved explosive success by military conquest across the Near East and North Africa--the Umayyads are in Cordoba (Spain) less than a century after Muhammad. The early years of Islam are characterized by an apocalyptic, messianic sense in which jihad is indeed a spiritual offensive. As I noted earlier, that doesn't necessarily mean forced conversion--secular motives like money were attractive. (Richard Bullitt has postulated that conversion occurred over time on a logarithmic scale, with the bulk of conversion ramping up in the 9th and 10th centuries). It did mean Muslim rule and establishment of Islamic faith in new territories.

But--the expansion of Islam slowed. Christianity stubborned kept hold of northern Iberia; in the 9th century even Byzantium started making incursions into the Muslim Near East. That second example offers a prime chance to witness how historical events affect Muslims understanding and representation of non-Muslims. Our earliest Arabic sources portray Byzantium as a rival: some levels of hostility, but very respected. They are especially impressed with the political and economic importance of Constantinople, and of the splendor of the city's architecture. Once the Byzantines pick up some military action, Muslim writers ramp up their vitriol. They find new ways to label the Byzantines barbaric, amping up the rhetoric of horrid Byzantine morals.

Even in the Latin Crusades, when the Islamic world is under direct invasionary attack by 'barbarians,' individual Muslim governors sometimes allied with the Franks against each other. (Although the chronicles are pretty uniform in calling the Franks atrociously bad fighters...it's just, they have really good armor and weapons, shucks.) In the Fifth Crusade, which dead-ended for the West in a massively humiliating capture of the entire crusader army in Egypt, the Muslim force treated them rather well and allowed their release as long as they returned to Europe.

Unlike the later medieval Church, medieval Islam has no centralized body of law or dominant interpretation. It's characterized by a series of overlapping legal and theological schools of interpretation that jockey for ascendancy throughout the era. As the rate of expansion of Islam grinds down almost to a halt, scholars debate the meaning of jihad in a world that suddenly doesn't hold apocalyptic hope and expectation of triumph.

One line of interpretation emerges that divides the world into two: dar al-Islam and dar al-harb, the world of Islam/submission and the world of war. This spiritualizes the idea of jihad: it is defensive, a matter of protecting Islam and its people, rather than working to prepare the world for the messiah through conquest. Unfortunately, Mottahedeh and al-Sayyid, who've done a lot of the work on early notions of jihad, don't really talk about whether we can trace this spiritualization of jihad in specific contexts to changing treatment of non-Muslims under Muslim rule (i.e. did a focus on defensive jihad ever lead to increased conversions or increased signs of repression).

Medieval Muslims who did find themselves in dar al-harb, on the whole, don't seem to have taken this idea of defensive jihad into their military hands. There are some cases of localized rebellion in Christian Spain and Sicily, but isn't that what you'd expect of any conquered people feeling ill-treated? Glick and Meyerson have both discussed the ways in which Muslim revolts in Christian Spain don't have hallmarks of proto-nationalism, they're in fact rather similar to or overlapping with Christian peasant protests of unjust conditions as well.

The Muslims of high medieval Sicily, conquered by the (Latin) Normans, found themselves deported en masse to the Italian mainland at Lucera. And yet they still chose to fight for their homes with the local Christian army against the papal invaders. The Muslim community of the Christian-conquered Ebro Valley in Spain stubbornly insisted, through letters sent abroad and sermons preached at home, that Iberia was their home and they would remain there against all the calls of the zealous Almohads in North Africa to leave dar al-harb for the comfort of the Islamic world. (And it sure wasn't because of amazing generosity on the part of their Christian overlords, to be sure.)

And then you have to consider, of course, that most Muslims are just ordinary people trying to live their lives. Islam spreads in medieval West Africa almost by accident. Merchants from the Sudan and North Africa set up trade colonies of sorts in the Ghana Empire, common language (Arabic) facilitates trade, being Muslim allows you to tap into a global trade network...By the time Ibn Battuta makes it to Mali in the 14th century, he's treated to a full recitation of the Quran (in Arabic) while amusedly observing cultural differences in the practices of individual Muslims between Mali and elsewhere in the Islamic world.

Overall, then--if we can even talk about an "overall"--it's a complex picture that depends heavily on specific historical contexts. The status of Islamic expansion, the school of law or theology, military developments on both sides, messianic expectation, the passage of time, geographic, economy, the goals of individuals: so many factors in the matrix, so many experiences we can identify in concrete times and places.