Final answer:
The crusading movement both strengthened church influence and caused power struggles, ultimately leading to a degree of secularization of church authority.
Step-by-step explanation:
The crusading movement, encompassing campaigns in both Iberia and the Levant, had complex repercussions on the relationship between the Christian church and the rulers of western Europe. While the Crusades initially indicated the papacy's growing influence and fostered a sense of unity among Christians, they also led to power struggles that strained church-ruler relations. Monarchs increasingly pursued their national interests, leading to the development of strong centralized powers that often operated independently or in direct conflict with ecclesiastical authority. Hence, both options a and b have valid points. The secularization of church authority was also a longer-term consequence of the Crusades. As crusading became institutionalized and taken up for various regional conflicts, kings often needed the papal support or indulgences that the church could provide, but simultaneously they built powerful bureaucracies and military capabilities that operated separately from ecclesiastical control.