Hildebrandt, later pope Gregory VII is remembered today mainly for excommunicating Henry IV of Germany for investing bishops, which forced the king to humble himself at Canossa on the 28 January, 1077. He is also, at least since Augustine Fliche's La Reforme Gregorienne, the eponymous proponent of Gregorian reform (although he did not instigate it nor see it through). This division of Gregory's policy into internal and external Church matters is synthetic, since there is no evidence Hildebrandt saw opposition to clerical marriage, simony and nepotism on one hand and lay investiture of bishops on the other to be separate issues. One clear example of this is found in his letter to the people of Germany, urging them to replace the unrepentant Henry IV with a new king who would not be surrounded by simoniac advisors. Anna Comnena, writing in Constantinople six decades after the pope's death, merges the two completely, explaining the conflict as stemming from Henry's simony and investiture of unworthy bishops and Gregory not seeking confirmation of his election with the king (in line with the reform movement's program).
At the time, the papacy had to rely on external guarantors against its Longobard or Muslim enemies. Those were Byzantium, then the Franks and finally the rulers of the Holy Roman Empire. In the 1040s the papacy was threatened by a rogue power rising in the South, the Normans, who effectively ended Byzantine control of South Italy and even captured the pope himself in 1053. The mutual excommunication of cardinal Humbert, papal legate to Constantinople, and patriarch Celurarius in 1054 is well remembered, as it has become the site of schism between the Latin and Greek Church. What is less known is that the legation's pragmatic objective was to secure an anti-Norman alliance, at which it failed.1 The death of Henry III in 1056 ad his heir's juniority left the papacy without options. In 1059 a synod held at Melfi, the Norman capital, saw Robert Guiscard invested with the title: 'By the Grace of God and St. Peter, duke of Apulia and Calabria and with their help soon of Sicily.' This forced marriage was not to be a peaceful one: the Normans had their sights not only on Sicily but also on the Epirus: although this was probably not obvious at the time, the papacy could either have good relations with the Normans or the Byzantines, whose waning strength the former wanted to exploit.
The papacy's uncomfortable position contrasts with the confidence and energy with which Gregory VII set out to re-establish and pursue the legal claims of the Holy See. When writing to Spain, Hungary or even Corsica, Gregory VII affirms that those lands were under papal protection. And so for example in 1074 he reprimands Solomon of Hungary for receiving the kingdom as a fief from the king of the Germans, since that crown was not the kings but the pope's to bestow. Lacking hard power, Gregory tried to use his authority to act as an arbiter between monarchs, for example exhorting king Olaf of Norway not to facilitate the division of Denmark. However his overconfidence could lead to being outmanoeuvred also on the plane of authority, like when Geza of Hungary, Salomon's rebellious cousin, not receiving a crown from Gregory VII, who was still hoping for Salomon to abandon his pro-German stance and submit to papal authority, crowned himself with a diadem obtained from Michael VII under unclear circumstance. His coronation took place a few months before the pope authored the letters that concern us and although Gregory VII makes no reference to the coronation, he probably knew about it. Gregory's "game of crowns" can be seen as the tool by which Western, Latin Christianity sought to exploit the deep crisis of the Byzantine empire, which suffered a crippling defeat from the Seljuk Turks in 1071 at the battle of Manzikert.
All this makes for fascinating reading and I have compiled a short reading list for you, with most of the below being publicly accessible. Below is also a link to a timeline to help orient yourself in the complex political landscape of the time. Have fun!
https://time.graphics/line/566099
Further reading
Chadwick, Henry, East and West: The Making of a Rift in the Church; From Apostolic Times until the Council of Florence, (Oxford, New York, 2003)
Cowdrey, Herbert, Pope Gregory VII; 1073-1085, (Oxford, New York, 1998)
Erdmann, Carl, The origin of the idea of crusade, transl. Marshall Baldwin, Walter Goffart, (Princeton, 1977)
Odlozilik, Otakar, 'The contest for East Central Europe in the eleventh century', The Polish Review, Vol. 2, No. 1 (Winter, 1957)
Rowe, John, 'Paschal II, Bohemund of Antioch, and the Byzantine Empire', Bulletin of the John Rylands Library, 49:1 (1966)
