There is another thread that attempts to explain history as more closely “deterministic”. And over long time periods this seems reasonable. CF guns germs and steel.
I doubt it made much difference to progress. Having knowledge locked up without the culture that made it is not that helpful.
On the other hand, the destruction of Baghdad by the Mongols had far reaching impact. Not only were the books destroyed (supposedly the river ran black with the ink of all the books tossed into it) but the populate was massacred (after which the river ran red with blood).
This had a profound effect on the Arab/Muslim world that I think is still felt to this day.
Dan Carlin has an episode on what he calls the Celtic Holocaust, the conquest of Gaul (ie modern day France). It's called this because it's estimated a third of the population was killed in the process. From a historical perspective, Caesar also could've lost here, which again would've massively changed history. There would be conquering and settling of Britannia without Gaul. And Britannia was important for many Roman emperors after that (eg Constantine, who converted Rome to Christianity, was proclaimed emperor by his troops in modern day York).
Anyway, part of what drove the Roman psyche with Gaul was that early in Roman history (the 4th century BCE IIRC), Rome was sacked by the Gauls. It's why we don't have much history before this and why the origins of Rome are shrouded in mystery and legend (ie most view the tales of Romulus and Remus as apocryphal at best).
But historians make the case of why conquering Gaul was so important to Rome. I was reminded of this when you mentioned the conquest of Baghdad. The damage can be well beyond the loss of culture or literary works.
Current Spain and Portugal's territory required from Rome no less than 190 years of wars. Romans kept going on submitting a few tribes there every year for two centuries.
A sort of "proof" of this assertion is that Rome, in the end, conquered all territories around the Mediterranean Sea and far beyond. Of course, the course of events are by nature unpredictable but I find it reasonable tosay that the odds for a long term victory of Gaul were slim.
However, but that was much earlier, the two Punic wars against Carthage were much more existential threats to Rome.
For those who bring up the positive effects of such a figure (Alexander spread Hellenism, Genghis created the Pax Mongolica), Carlin said that these were not intended by such figures but simply happened as a result of their statecraft. Alexander for example did not expressly conquer peoples in order to spread Hellenism, he did so because he was expected to as being the son of a king.
People simply have a recency bias as a default cognitive effect. One day, Carlin says, someone will also write about the positive effects of the Third Reich, just as they write about Alexander and Genghis, once all the people who might have been affected have died off.
https://jewsforjesus.org/learn/the-messianic-time-table-acco...
Something Dan said has really stuck with me. He says that science is less interesting. If you don't invent a light bulb, someone else will. It's inevitable. Science can of course impact history (eg the development of the atomic bomb) but a lot of other events could go either way and it dramatically changes history.
IIRC Cyrus (one of the great Persian kings in that podcast) ordered the rebuilding of the Temple Mount and probably singlehandedly saved Judaism from extinction. Had that died then would we have had Christianity and Islam?
The Battle of Marathon was the major turning point that allowed the Greeks to survive and obviously go on to impact the Romans and really the rest of Europe. How different would history have been if the Persians had won and Europe had become Persian?
[1]:https://www.dancarlin.com/hardcore-history-series/