This is just about the longest war in human history actually undertaken for a purpose.
During that long war the strongest most powerful non-Moslem nation in Western or Northern Europe was a consortium of Brythonic Celtic speaking principalities located in what are now called Cornwal and Brittany. It was customary for 2, 3, 4, 5th sons of nobles to ship out to Spain to join in the Reconquista for the purpose of gaining glory, farmland, towns ~ and rank. Today an incredibly high percentage of Spanish noble names are actually Cornish or Breton sentences that relate to formal occupations or positions taken during cavalry line ups!
Too much credit is given to Charles Martel ~ he was a layabout who drank too much and had too many wives. The real knights who won Spain were from that other place!
A regular objective of the Christian knights was to find a library and seize it. Once done the Catholic Church and wealthy magnates would sendin scholars to review the books and send them North to be copied and distributed throughout Europe. Several such libraries over the centuries were sufficiently well stocked to allow Western Europeans in the Northern redoubts (Belgium) to initiate INDUSTRIALIZATION!
Spain itself had as close to an industrialized population as any nation up to the 1300s in Belgium ~ anywhere in the world ~ the people staffing it were called Jews. Medieval Sephardic names frequently reflect a Jewish industrial occupation ~ e.g. Schmidlap(spelled many ways) Is a ladino word meaning 'sheet maker/painter' ~ in effect, someone who made paper. And who can forget the famous Bookbinder family ~ and so forth. (That's only a sample ~ anyone who already studied latin or spanish can go learn ladino on the net and get into this ancient language ~ it explains so very much about Catholic and Jewish history in Spain)
Whatever else Europeans were doing to each other politically or economically, when it came to the war against the moors, they were all in it together. As Protestantism rose, both Catholic and Protestant soldiers went to fight the Turks in the Balkans, or along the Mediterranean shore ~ Captain John Smith was a veteran of those wars and understood Turkish. He was selected to head up the Virginia colony because it was believed Turkish was in widespread use already on the Eastern seaboard ~ which it was, in a way. The Spanish sent many of their POWs captured in Mediterranean battles to a POW camp in South Carolina!
From the grandest palace to the most humble mud and stick hovel, Europeans were, in fact, united against the Saracen in ways we can scarcely imagine for most of that 700 years.
The recurring theme one hears from muslim apologists is that the Crusaders were the offenders. They somehow ignore the fact that within one hundred years of muhammad's death islamic armies were invading Spain and France - 4,000 miles from Saudi Arabia and 350 years before the First Crusade.