Here was an opportunity.

With sixty thousand Norman adventurers like himself, William started with the desperate purpose of invading England and wresting the crown from his cousin Harold.
It was not the first time the Northman had invaded England.

But never before had he come bringing a higher civilization, and under the banner of the Church! In a few weeks Harold, last king of the Saxons, was dead, and William, Duke of Normandy, was William I., King of England.
Philip, King of France, saw with dismay his richest province ruled by a king of England, and his own vassal wearing a crown with power superior to his own! A door had thus opened through which would enter entangling complications and countless woes in the future.
While William was trampling England into the dust, and with pitiless hand rivetting a feudal chain upon the Saxons, another and greater centre of power was developing at Rome, where the monk Hildebrand, who had now become Pope Gregory VII., claimed a universal sovereignty from which there was no appeal.

Christ was King of Kings.

So, as His vicegerent upon earth, the authority of the pope was absolute in Christendom.
The moment of this supreme elevation in the Church was reached at Canossa, 1072, when Henry, the excommunicated Emperor of Germany, came barefooted, in winter, and prostrated himself before Gregory VII.