Why so long time?

 One might wonder why it took so long for Christian Europe to strike back against Islam.

In 637 there was no Pope with an army, no France, no England, no Germany as we know them.

The West was fragmented into small Germanic kingdoms. The Franks under Charles Martel and Charlemagne were busy fighting to survive against Muslims in Spain / southern France and against pagans in Saxony.

The Frankish Carolingian Empire split up in 843 and then collapsed into Viking, Magyar, and Muslim raids for another century. From 900-1050, Western Europe was on defence everywhere.

There was no logistical ability to move an army 3,000 km to Jerusalem, feed it, and sustain it. Armies were small, seasonal, feudal levies.

I read in one book that western sources from the 8th-10th centuries describe pilgrimages to Jerusalem without major interference. As long as pilgrims could go, there was no popular pressure in Europe to "liberate" the city. Jerusalem was important theologically, but it was not under a perception of acute desecration.

But as I wrote in another blogpost, things changed dramatically.

At the Council of Clermont in November 1095, Urban II turned Alexios's request for military aid into a pilgrimage armed with the promise of remission of sins - to free the Eastern churches and liberate the Holy Sepulchre. That ideological framework - crusade as armed pilgrimage - had never existed before 1095. Without it, a European army marching to Jerusalem was unthinkable.

So it wasn't a 458-year wait. It was 400 years of impossibility, followed by about 20-25 years after Manzikert when a new Turkish threat made the old arrangement collapse and a new Western political-religious structure made a response possible.