Final answer:
The Catholic Church was the largest institution in Europe during the Middle Ages, exerting significant spiritual, political, and economic influence until the Protestant Reformation began to challenge its dominance.
Step-by-step explanation:
During the Middle Ages, the Catholic Church was the largest and most influential institution in Europe. It wielded immense power not just spiritually but also politically, economically, and socially. The Vatican in Rome, through the Church, exerted control over various aspects of life including learning, scholarship, and finance, as it levied taxes on the faithful. Moreover, the Catholic Church was central in providing a unifying religious structure that linked Christian Europe even as political entities like the Holy Roman Empire, Italian city-states, England, France, and Spain emerged and evolved their political powers. Despite attempts to reform the Church and the eventual break due to the Protestant Reformation, sparked by figures such as Martin Luther and John Calvin, the Catholic Church remained the most powerful international organization in Western Europe until the Reformation.