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At what point did the idea of knights from Western Europe joining together to form an order against some kind of Islamic foe become viable/plausible?

I understand the direct causes of the First Crusade come from Seljuk attitudes towards Christian pilgrims following the Battle of Manzikert, with several other long - term causes too.
However, when did this idea first become a realistic possibility? Ignoring why they would do it, let's imagine the Pope calls for a Crusade in an earlier century than the 11th, would it have worked?
Was there something about Europe in that period that allowed the Crusades to occur, was there an excess of young noblemen or an increase in power of the papacy? Structurally, would it be possible for a Crusade to happen before.

And not just in the Middle East, could a Holy Order of knights be formed in Iberia in an earlier century, maybe not as popular as the OTL Templars or Hospitallers, but could such an Order exist? Maybe not due to the internal politics of all the Christian Iberian realms, but are there scenarios where they could exist financially, manpower wise, etc?
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