The Christian Crusades were primarily a consequence of a complex geopolitical situation, a multi-century of clash of empires (in particular the Ottomans, Ummaya

The Christian Crusades were primarily a consequence of a complex geopolitical situation, a multi-century of clash of empires (in particular the Ottomans, Ummayads and the Byzantines) across multiple theatres from modern Spain to Jerusalem and beyond. The real role that Christianity had to play in this clash was as the great unifier for a fractious western Europe wreaked by petty kings squabbling among themselves, turning their violence outward against common geopolitical foes rather than inward against each other. A pagan Europe would still have seen similar wars, it just would have had a harder time unifying to repel the encroachment of the eastern empires.