The Byzantine Christians were pushing the muslim vampires back for hundreds of years before the first crusade.
Specifically the wars between the 7th and 12th centuries AD
Eleni, I don’t think the author neglected that. The article was about putting the Crusades in perspective. Information about the eastern Christians was given just insofar as it related to that goal of placing them in perspective. The article was not about the eastern Christians.
However, the author did mention that the Byzantines had already had most of their land conquered by the Muslims. That made it plain that the eastern Christians had long been fighting with them.