The uneasy relationship between church and state dominated the Middle Ages and has continued into modern times.
In the 11th century, during the reign of Henry III as Holy Roman emperor, the split between East and West was formalized when the pope at Rome and the patriarch of Constantinople excommunicated each other. Division had existed for centuries, but this was a formal break that still remains. It has had major political consequences throughout history. More recently, the East-West divide of the Cold War arguably had some of its roots in the church split of the 11th century. Additionally, the ethnic conflict in the Balkans in the 1990s goes back to ancient religious rivalries.
A major struggle between Germany and Rome was started by the Lateran Council of 1059, which decreed that future popes would be elected by a college of cardinals, removing the influence of the emperor. This was to have a long-lasting effect and was a portent of conflict to come.
The crowning of Charlemagne by Pope Leo III in A.D. 800 had led to a close alliance between church and state, which can be likened to a marriage. The church at Rome was considered the spiritual authority over men's lives, whereas the emperor was the head of the political organization to which men submitted. The church taught the people that they must obey the emperor, whereas the emperor enforced the authority of the church over the people in spiritual matters. It was the emperor's job to ensure religious conformity and the unity of the faith, with force when necessary.
Between them, they controlled most of the peoples of Europe for centuries. Only with the Protestant Reformation of the 16th century was any progress made toward religious freedom.
Pope Leo XIII, late in the 19th century, summed it up this way: "The Almighty has appointed the charge of the human race between two powers, the ecclesiastical and the civil, the one being set over divine, the other over human things." He also said: "Church and State are like soul and body and both must be united in order to live and function rightly."
