This work examines the complex relationship between Church and State from the Middle Ages to the modern era, focusing on the interaction between political and spiritual powers in European history. During the Middle Ages, the Church, under the papacy, asserted its dominance over secular rulers through doctrines like the Two Swords theory and conflicts such as the Investiture Controversy. The balance of power shifted between popes and emperors, with the papacy reaching its zenith in the 13th century but gradually declining due to events like the Avignon Papacy and the rise of national monarchies. In the modern era, secularization and the rise of the nation-state further weakened the political influence of the Church. Monarchs asserted control over religious matters within their realms, while the Reformation and Enlightenment ideas reinforced the separation of Church and State. The evolution of Church-State relations continues to influence contemporary debates on secularism, religious freedom, and governance. By exploring key historical events, intellectual movements, and political transformations, this study highlights the enduring impact of Church-State relations on Western civilization and modern political systems.