What is relationship between the rulers of Europe and the Catholic Church during the Crusades?

During the Crusades, the relationship between the rulers of Europe and the Catholic Church was complex and often symbiotic. European monarchs sought the Church's endorsement to legitimize their campaigns and rally support from their subjects, while the Church aimed to unify Christendom against a common enemy, promoting religious fervor and territorial expansion. However, tensions could arise, as rulers sometimes prioritized their own political ambitions over the Church's directives, leading to power struggles and conflicts of interest. Overall, the Crusades marked a significant collaboration, albeit fraught with underlying rivalries.