Considering the possibilities for an alternative and less disastrous result for the Byzantines at Manzikert is perhaps the likeliest scenario that could avoid any call by Alexius I or another Emperor for a large-scale recruitment of Western mercenaries via an appeal to the Pope. The Byzantine army was by the 1060s too reliant on heavy infantry and heavy cavalry rather than light, fast-moving cavalry to be sure of victory in a large-scale encounter with a major Turkish army, as the latter had better (horsed) archers and so could both cause panic in their ranks in battle and cut off and decimate supply-trains in a long campaign in inland E Anatolia. An over-confident or poorly trained Byz army getting into trouble there was thus quite likely , given Saljuk tactics - but not its total defeat and the loss of most of what is now Turkey. The result of Manzikert itself was a close-run thing, as the Byz army was holding the enemy back for most of the battle despite being trapped in a mountain pass by mobile Turkish cavalry in larger numbers than they expected - the disaster followed a muddled order to retire to the Byz camp for the night at the end of a day's clashes causing a section of the Byz army to think that their retiring colleagues were fleeing and panic and do so too. It was later alleged that the commander who panicked, Emperor Romanus' young co-emperor Michael VII Ducas' ambitious cousin Andronicus, did so deliberately to get his rival Romanus defeated and ruin his reputation.
The Saljuks then moved in to break the Byz up and surrounded and captured the Emperor, Romanus IV - who the Sultan forced to sign a treaty and give up some frontier land in dispute and then released. But this was not handing over all of Anatolia, just the frontier - the Saljuk mass-movement of tribes into the peninsula , and thus the disaster facing Alexius when he took power from Romanus' successors in 1081 by a coup, only followed the failure of the discredited Romanus to keep his throne after the 1071 war. He was deposed in a revolt started in the capital by the Ducas family of his young co-ruler, Michael VII (ruled 1067-78), whose mother Eudocia he had married in 1068 to stabilise the regime and act as its militay leader. (Romanus, a general, had never really been accepted by the Ducas or the civilian elite in the capital, and was always at risk from them.) This civil war, won by Michael's supporters , damaged the army further , as did more revolts against the Ducas family by alienated generals in the 1070s - and in 1078 a major revolt by a military junta, which suceeded, left western Anatolia open to invasion and helped the Turks further. Had the 1071-2 or 1078 civil wars not occurred, the Turks - moving into the region as separate tribes on their own initiative, not as one force directed by one Sultan (the Sultans were based in Iran and had other priorities, eg Syria, after 1072) - would not have gained nearly as much of the peninsula and Alexius would not have needed such a large Western army. For that matter, had Michael VII's cost-cutting civilian bureaucrat noble father Constantine X Ducas (ruled 1059-67) not been a poor general who neglected the Eastern frontier and did not adapt his army to 'hit and run' Turkish light cavalry raids, the chances of a Byz defeat at Manzikert would have been less. Or else, another major possibility , Constantine might not have become Emperor at all - his predecessor was a far better and more vigorous ruler, and a capable general, ie Alexius I's uncle Isaac Comnenus , who did start to reform the army but had to retire to a monastery in 1059 after a two-year rule due to ill health (and had n son). Had he lasted longer - he was in his late 50s then - and had a son, or passed the throne to his brother John (Alexius' father) and then to John's eldest son Manuel (d 1071), the possibility of disaster at Manzikert, miilitary collapse in the 1070s, and a major need of Western help would have been less.