Why were there no significant crusades launched by (western) European powers in the over 400 years between Isam's rise and takeover of Jerusalem from the Byzantine Christians in the 7th century until the First Crusade at the close of the 11th century? I suppose you could call a lot of the Byzantine efforts to fight back a crusade of sorts, as was the early Reconquista in Spain, but I'm talking about things on the scale of the main Crusades
- Was it not a real problem for Christian pilgrims that the Umayyad Caliphate took over? Did they not actively cause issues for them until the age of the Seljuk Turks and such?
- Were there not powerful enough or sufficiently well-organized states capable of projecting the kind of power necessary at the time?
- Was there lack of unity among powers like the Franks, Visigoths, Lombards, Saxons, etc to do this?
- Was Christianity not even widespread enough until after the Viking age?
- I also take it the Popes in the first millennium were not as powerful, influential, and independent as they would later become around the time of Gregory VII and Urban II? During the "Byzantine Papacy" many were in effect subservient to Constantinople or appointed by it I think
- Either way, what were the reactions of central and western European peoples to the rapid Muslim capture of the Holy Land in the 7th century? Did they not see it as an immediate threat, and only came to do so later after the fall of Spain and subsequent battle of Tours with Charles Martel in 732?
- Was the launch of the actual Crusades more of an opportunistic power move by the Pope because the Byzantines needed or asked for help from the West against the Turks?
It's a tough question to answer, but you've proposed a number of likely explanations. Despite the rise of the caliphate, the majority of people living under Islamic rule were probably Christian, perhaps until the 1200s or so. The Carolingian empire was perhaps the most successful early medieval state, and the forces pulling it apart proved stronger than the ones holding it together (arguably this began under Charlemagne himself and certainly under his son Louis the Pious), so there was no real basis for state-led or even state-sponsored overseas expeditions. When we turn to ethnic titles like Visigoths or Saxons, medieval rulers experimented with these terms but its doubtful that they ever really worked as labels that could communicate a useful sense of political identity. Early medieval popes sometimes attracted attention, especially Gregory the Great, but papal authority generally consisted of approving things done by bishops elsewhere and occasionally getting chased out of Rome by angry mobs (such as Leo III). So it seems like a lot of the main factors that made the Crusades possible simply weren't there in the early Middle Ages.
What were reactions to the rise of the Caliphate? They were pretty sketchy at first, and early written accounts suggest people elsewhere didn't entirely understand what was going on. That makes sense, since the 600s was a time of limited communication and commerce over long distances. Western commentators tended to understand Muslims alternatively as pagans or as heretics, but people in the Near East might have even been relieved to see the constant fighting between Byzantium and the Persians disrupted. Attitudes in Spain were, of course, more complicated following the Muslim takeover in the early 700s, by which point the caliphate was really starting to consolidate into an impressive state—notably a state in which Christians had a sort of protected status as a People of the Book.
Much has been made about the battle of Tours in 732, but only in retrospect do we see this as a clash-of-cultures type moment. In fact, I think few scholars actually see it as a clash-of-cultures moment, despite popular references to the battle. Charlemagne, for example, was excited to get delegations from both the Byzantine emperor and the Abbasid caliph after his own coronation in Rome, suggesting that his political circle considered the three rulers to be sort of co-heirs to the classical Roman empire (an opinion I share). I doubt there's any connection whatsoever between Tours and the later Crusades, although popular poetry about the defeat of a Carolingian expedition into Spain (The Song of Roland) did capture later medieval imaginations and may have helped foster enthusiasm—though Charlemagne and his contemporaries did NOT treat it as a stimulus to further fight with Muslims in Spain, much less in the Holy Land. Charlemagne was much more interested in campaigning against and eventually ruling over the neighboring Saxons, and the idea of a Reconquista was a much later development, perhaps the 1200s, I believe.
My impression is that the early Crusades were facilitated by a few phenomena that we rarely see in the early Middle Ages—the consolidation of both royal and papal power, rising competition between the two and efforts to find common projects, the ability of charismatic leaders (e.g. Bernard of Clairvaux for the Second Crusade) to exercise outsize influence, and political infighting within the caliphate that made the crusades possible. The Byzantine ruler did, of course, feel pressed, but on balance the Crusades might have been more trouble than they were worth from the Byzantine perspective.
The Crusades are an area with lots of study (and I suspect a fair amount of enthusiasm on this sub), but Crusades specialists might understandably have little to say about why crusades didn't occur earlier. It's a counterfactual type of question that can't be answered with much certainty. Instead, you might consider reframing your question: "What particular factors made the First Crusade possible in the 1090s?" And you might clarify that you're not looking for the precise chain of events (which is debatable) but rather the broad conditions and developments that made both the call for a crusade and efforts to answer that call possible in the 1000s.