An interesting question that comes out of this is....What the hell happened to intellectual advancement in the Islamic world from 1100 to the 20th century ? I'm not much of a history buff, but have always been curious why it lagged behind Europe so much during much of that period ?
There are a huge range of opinions on this. The classic 'Orientalist' view was that Muslims got complacent, and convinced of their own superiority they felt they had nothing useful to learn from infidels beyond military technology. This is not really accepted by today's historians, who point to, for example, the amazing cultural achievements of the Ottomans, Safavid Iran, and Mughal India deep into the 17th century (e.g. the Taj Mahal was completed in 1648).
One factor commonly cited by mainly Arab Muslims of a nationalist leaning in the last century and a half was that the ascendency of the Turks in Islam, with their martial traditions and lack of intellectual curiosity, stymied the further development of Islamic civilization. Something not much talked about anymore is that from around the mid-9th century onwards, the major Islamic dynasties were often ruled by Turkish slave-soldiers who lived very much in isolation over the Arab and Persian populations they ruled, and who valued power and stability over the kind of free-thinking which generally helps drive intellectual achievement.
On the other hand, some historians believe the coming of the Turks actually helped not only to save Islam (the Mamluk Sultanate in Egypt, which is the supreme example of a Turkish slave-soldier dynasty, expelled the last Crusaders from the Syrian coast and defeated the Mongol advance west from Baghdad), but also to spread the faith into new lands, most notably Anatolia and India in the 11th century, and south-east Europe from the 14th century onwards.
Another obvious factor is the change in the world's economy produced by the European voyages of discovery. Not only did the discovery of the Americas saturate the world's gold market, driving prices down at the expense of the Middle East, but the Indian Ocean trade was diverted around southern Africa, cutting out the large Islamic landmass sitting between Europe and East Asia where Muslim merchants had acted as middlemen. The associated loss in profits could only have hurt the progress of Islamic culture.
I would say that pinpointing one particular event, such as the destruction of Baghdad or the Crusades, does not help explain much. The Crusades in particular had very little effect on Islamic civilization, confined as they were to a very small part of the Islamic world. It's only really in modern times that Muslims have become focused on the Crusades, as they seek to draw parallels with modern European imperialism. But at the time, they were regarded as a minor episode. The Mongol invasions were obviously a major event - Ibn Taymiyya, who ISIS guys seem to regard as semi-divine, wrote his major works in the aftermath of the Mongol destruction of the Middle East, hence his gloomy worldview. On the other hand, the Mongols soon embraced Islam, and helped to drive the post-1258 cultural advancement which peaked in Mughal India.
It should always be remembered that the apparent 'decline' of the Islamic world vis-a-vis Europe is hardly unique, it's something all the major civilizations (China, India, etc.) have had to grapple with since the rise of Western power.