Yea, at the time of the first crusades the Fatmid Arabs sided with the invading Franks over the people they considered their real enemies, the Seljuks. I believe they sent peace envoys and attempted to negotiate a power sharing arrangement of sorts before the fall of Antioch. It wasn’t as if Islam had a united front that was on the brink of sweeping across Europe.
Not at that time, to my understanding. But it’s also true that threats to Europe came in waves with lulls in between. At the time of the First Crusade, the Empire was threatened, not by the Arab Muslims, but by the Turkic Seljuks. It wasn’t an imminent threat, but the Seljuks had recently taken a lot of the Empire’s territory, and it wasn’t looking very good for the Empire as a sort of chronic thing.
One could question whether the Franks would have initiated the First Crusade for the sake of the Empire, because the East/West relationship wasn’t all that good, before, during or after. But the Empire did regain a lot of its former territory thanks to the First Crusade. The Byzantines wanted Palestine back too, but the Frankish leaders ignored that part.
One of the huge ironies of all the invasions (and there were several) was that the Ottomans possibly saved Europe from Timur and Timur possibly saved Europe from the Ottomans.
Possibly the saddest irony of all is the evident belief of the Arab Muslim world that “Crusaders”, then and now were and are their primary enemies. In reality, their “caliphate” and all the dreams they have about it, was ruined by invaders from Central Asia, not from the West.
Interesting and ironic too is the fact that the biggest threat to the “caliphate” dream is now Iran, not the West. (another recurring theme) But I think the Sunni state leaders, not “caliphate” dreamers themselves, realize that Iran is the greatest existential threat to anything they want for the future. So, of course, do the Sunni Jihadis, which is why they’re pouring into Syria. The Jihadis, of course, want their “caliphate”, but the Sunni state leaders, who don’t, also realize Iran is the great threat, and fund the jihadis for now as a totally untrustworthy “mercenary army”. One remembers the story of the “mercenary” Mamluks employed by the Fatimids. That didn’t turn out too well.
Ironically, the Sunni Arabs might eventually bemoan the departure of the West from the Middle East just as many hated to see the Crusaders go. Many, of course, already do.
The “Franks” (some Arabs still call Westerners that) were and are the best resource the Arab Muslims had for defense against stronger neighbors. But like the Crusaders, we left the place to the slaughter that was inevitable upon our departure.
The Crusaders, of course, had no choice but to leave. We did have a choice.