Pretty sure that was the plague of Justinian which was y. pestis
iirc. There have been many others taken down by smallpox. It's amazing to me how dumb people were to oppose the smallpox vaccination and elimination campaign. That one virus did more damage to us as a species than all our wars combined, and it along with plague are two of our species most mortal enemies that always had been holding us back.
Really the entire bedrock of modernity is a combination of fossil fuels and modern medicine, and you needed both. If you have one without the other you basically just plunge back into a more comfortable medieval era. Empires were frequently stricken by one pox or another, and often one calamity followed in footsteps of another which is why Pestilence's companions were famine, war, and death. Spanish flu and black death both followed war which helped incubate and spread them everywhere, followed by surging through economic routes like arteries into every major urban zone and outpost. Where a pestilence began first, often food supply would collapse, it would trigger the roiling strifes to boil over into open war. Any one of these things could take down a decaying empire, but the combination of all three will often spell the doom of the old order.
Now that I think about it I dont know what took down different caliphates and Islamic empires. I do know for sure though that the Black Death was the second major plague epidemic, with most scholars seeming to agree that the 7th or 8th century Plague of Justinian was the first known recorded outbreak.