Generic my foot, that was based on multiple analyses on the state of the Byzantine Empire on the eve of the Muslim onslaught. When entire provinces welcome a foreign, heathen invader as a preferable alternative to the Emperor and the particular interpretation of Christianity he has opted to sponsor as the "state religion" (for the Muslims didn't particularly care a whit about how exactly their new Christian subjects worshipped), the realm has some real structural problems. And the geostrategic vulnerability is very much a fact; aside from the "natural fortress" of Anatolia - where the Empire indeed fell back to for quite a while - it was painfully short of "naturally defensible" borders, in particular in the dangerously immediate vicinity of the capital itself in the Balkans.
Anyway, as I seem to recall mentioning, Byzantium enjoyed numerous periods of resurgence. And all due credit to the rulers who pulled that off, despite the realm being almost constantly under assault from all directions. Didn't really matter much in the end, though - and equally, it suffered from any number of disastrous downturns due to both internal problems and external aggression (Fourth Crusade being arguably the one with the most serious long-term repercussions, as the Empire never quite fully recovered from that one).
Also your OP seemed to be mostly about the "Christian West" rather than Byzantium, so I kind of didn't look too closely at it given that I'm not even addressing that particular topic... (Your *second* post seems to be a short rebuttal to Lazy O for "trolling", so yeah...) I'd point out that to argue that "teh Muzlums" demolished the Roman Empire is BS right on the face of it, though - for the faith didn't even exist yet when the ailing Western Empire collapsed under the Germanic migrations, and the Eastern Empire (AKA "Byzantium") went on truckin' for a whopping eight centuries or so after losing the Middle East to the Arabs...
For another, awful many people here seem to be merrily ignoring the little detail that Muslim scholars didn't just copy Classical junk, they actively elaborated on it; a fair bit of which eventually made its way into Western Europe, AFAIK primarily through "interface zones" like Sicily and Moorish Spain, where quite a few Christian literati went to study (and during the Reconquista captured Moorish libraries couldn't be looted and translated fast enough, as far as the scholars were concerned). In all fairness, the same goes for the much-maligned Catholic Church which in actual fact was the main refuge of higher learning and advanced thought in Europe, as well as the birthplace of the university.
And as for the Great Library of Alexandria, spare me. By the time the Arabs turned up there was little more than a distant memory left of the thing.
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