Describe the historical background of the "Disgrace at Canossa" based on the Letter of Gregory VII to the German Princes & Henry IVs Oath of...

In Pope Gregory VII's letter to the German
princes dated 28 January 1077, the Pope describes the penance and absolution of the Holy Roman
Emperor Henry IV. The Pope and the Emperor had been embroiled in a dispute known as "the
investiture controversy" about who had the authority to appoint bishops, and this had
culminated in Gregory excommunicating Henry at the Lenten synod of 1076. Henry then sent
messengers to the Pope, promising obedience. He finally came to Italy himself and approached
Gregory at the castle of Matilda of Tuscany in the town of Canossa, where he was staying. There,
Gregory writes, Henry stayed for three nights outside the castle having laid aside all the
trappings of royalty, with bare feet and dressed simply in wool, crying and imploring the Pope
for the apostolic blessing.

At length, Gregory continues, he "loosed the
chain of the anathema and at length received him into the favour of communion and into the lap
of the holy mother church." This affair, for the time being, consolidated the power of the
Pope and resolved in his favor the long-running struggle for power with the Holy Roman Emperor.
Henry had to swear an oath that he would effectively be the vassal of the Pope and "either
do justice according to his judgment or conclude peace according to his
counsels."

The letter and the oath are both attached
below.

href="https://avalon.law.yale.edu/medieval/inv08.asp">https://avalon.law.yale.edu/medieval/inv08.asp