Final answer:
The Pope lost influence in the late Middle Ages due to military defeats in the Crusades, internal corruption, religious conflicts, and the rise of nation-states. The crusading ideal declined as papal power waned and royal power resumed, with holy wars being called for political rather than religious purposes.
Step-by-step explanation:
In the late Middle Ages, the Pope and the Catholic Church lost influence as a result of several factors including military defeats to Islamic armies during the Crusades, internal corruption and conflicts within Christianity, and the rise of powerful nation-states. Crusading itself declined in popularity due in part to the decline of papal power and the revival of royal power in the fourteenth century.
The Crusades, which were initially launched by popular, reform-minded popes to reclaim Jerusalem from Muslim control, ended up causing internal strife within the Christian world. The persecution and eventual disbandment of the Knights Templar by the French king, who accused them of blasphemy and apostasy, was a significant blow to the papacy's influence. Additionally, the emergence of centralized governments and the rise of new Islamic powers like the Mamluks and Ottomans made further crusades impractical.
Theorizing the conflict between Byzantine and Seljuk as a fight between religions, Pope Urban II inadvertently set the stage for a series of religious wars. The perceived necessity for holy wars transformed over time, with popes calling crusades not just to liberate holy lands but also to combat perceived enemies of the church, including non-Christians in the Baltic and heretics in France. Over time, the concept of crusade became woven into the political fabric, often serving the interests of kings and monarchs more than religious or spiritual objectives.