The Mongol seige of Baghdad was particuarily bad due to the destuction of irrigation canals, and uprooting of date palms. This made any sort of agriculture extremely difficult. As for the destuctivenss, it was more thorough than others but not exceptionally so. Combining this with the deaths of large amounts of the population and there arises an inabilty to repair the agricultural systems, leading to an ultimately worse situation than other conquered cities. Sources vary wildly on the number of deaths, from 100 thousand to one million.

Baghdad was a major hub of Islam, and science at the time. It was lead by Caliph Al Musta Sim. Before the seige the Mongols armies lead by Hulagu were involved in conflicts with the assasins in Iran. The Mongols asked the Caliph for assistance, but he did not comply, and instead sent mildly insubordinate responses to Hulagu. (Dont piss off the Mongols) combined with other incompitancies of the Caliph and his advisors Bagdhad was not prepared for the Mongol army.

The Mongols absolutely appreciated, and even embraced new technologies and beliefs. Had they not used the seige technologies they discovered in China, their conquests may have been unsuccesful, and likewise with religous acceptance. The Seige of Baghdad was a bit different. The executions spared no one, where in other conquests, skilled laborors, warriors, and leaders would have been used. The Grand library f Baghdads books were thrown into the Tigris river, ruining valuable texts from some of the greatest minds of the time. Survivors said that the rier ran black from all of the ink. I feel the exceptional thing here is not that they were actively trying to destroy knowledge, but rather the knowledege they destroyed was a consequence of the attempt to "teach a lesson" by utterly devasting the city due to the Caliphs actions.