The first Holy Roman Emperor, Charlemagne, ran the empire. No one contested that, or if they did, apparently it wasn’t for long. He had, let us say, a dominant personality and decisive way of settling inter-personal disputes. However, after his great-grandsons divided the empire (the Franks had partiable inheritance, so each male had to get land), the role of the emperor dwindled as more powerful nobles gained territory and control, and the internal politics of Rome started to resemble a Mafia soap opera. It took the Ottonians, and what I half-jokingly call Holy Roman Empire 2.0 for the emperor to return to a place of political prominence and authority, and even then he had a lot of challenges from nobles who preferred their feudal overlord to stay both weak and far away.
With the Ottonians came several changes. The kings of France, or rather the Frankish kings, had grown strong enough that they stood on their own, outside the empire. The Ottonians were from the German-speaking lands, and their power base was the middle Rhine Valley, the Main River lands, and over around the Harz Mountains. Like Charlemagne and his successors, the Ottonians moved around a lot, but their “base of operations” was in Goslar, in the mountains to the east, where the newly-converted Saxons and the Slavs resisted imperial rule. The east had no memory of Roman leadership, not really. The Romans never stayed very far north of the Danube, and the Slavic tribes had pushed the Germanic peoples west and either north or south in the 600s-700s, as best we can tell. Or they intermingled with them (Austria, Hungary, Croatia). So the empire now faced east as much as south, fighting and establishing diplomatic ties, and fighting with, the Slavs and Saxons, and starting to move civilization north, into the wet, cold areas of what is now Lower Saxony, Westphalia, Schleswig-Holstein, and Mecklenberg-Vorpom. And parts of modern Poland.
Because the emperors were always on the move, more or less, and occasionally had to go down to Rome to settle things at least temporarily, the local nobles and imperial servants were tasked with running things on a daily basis, and had to be the first on scene when, oh, the eastern Saxons decided to revert to paganism and attack someone (not always in that order), or the Magyars invaded, or the Byzantine Empire deflected someone north and west. Also, most of the nobles were related through marriage or ancestry, and at any time, several had possible claims on deserving the title of Holy Roman Emperor of the German Nation. Depending on the personality of the emperor and which nobles had risen to power, this could lead to collisions, or to cooperation. Occasionally, the popes would wade into the fray, as Gregory VII did with Henry IV in 1075-76.
After the Ottonians came the Salians, another dynasty from the Rhine Valley, of whom Henry IV is the most famous, although he’d probably have happily relinquished that distinction. He ended up fighting with the major nobles, his son, the pope twice, and pretty much everyone else. Conflict management and resolution was not one of his strong suits. All this is a bit of a fog for most English-speakers, because we tend to focus on what was going on in Britain at the time – the Norman Conquest and other minor excitements. Also going on was the conversion of Poland to Catholicism, more or less*. Poland became Catholic as opposed to Orthodox, but because they were officially brought into Christendom directly by a Papal missionary from Bohemia, instead of from one of the Holy Roman Empire’s bishops, they were not considered part of the Holy Roman Empire’s lands. The relationship with the Emperor varied from “great friends” to “here we go again, call out the army.”
The emperor was supposed to be a neutral party above the nobles, someone who could mediate, settle arguments before they got out of hand, and who could balance the demands of the free cities with those of ecclesiastic nobles (like the Archbishop of Mainz) and the secular nobles (Saxony, Austria, Bavaria, Swabia, and so on.) He was also tasked with defending Rome and the pope (not always the same thing). Again, since the emperor was always on the move, and sometimes south of the Alps, that left a lot of wiggle room if a noble got ambitious.
Enter two real characters in every sense of the word. Frederick von Staufen and Heinrich of Saxony had nearly equal claims to the imperial throne. Heinrich came from the Welf family, Frederick from the Staufers**. They were almost the same age, and both tended to be, let us say, pugnacious. Frederick of the Red Beard (Barbarossa) ended up on the throne, and Heinrich swore feudal vows of vassalage, promising to help the emperor if needed and to obey – mostly. Their first collision came fairly early, when Frederick had Heinrich’s first marriage annulled after several years, in part because the property owned by the bride’s family surrounded Frederick’s own home base. Heinrich agreed, but he was not entirely pleased. He married the daughter of Henry II of England, which was OK. Yes, that Henry II. Family get-togethers must have been entertaining to watch from outside stabbing range.
The far north of the German lands, notably along the Baltic and eastern North Sea, and been depopulated by the Northern Crusades, and years of Viking raids. Heinrich turned his attention north, and while Frederick was going to Jerusalem and doing things in Italy and elsewhere as well as in the German lands, Heinrich refounded Lübeck, founded Luneberg and Braunschweig, and encouraged other settlements to expand. He established Braunschwig (Brunswick) as his main base. Once or twice, Frederick deputized Heinrich to deal with things while Frederick was tied up in Italy or dealing with Seljuk problems. However, Heinrich grew very powerful, and rather independent. Eventually the two collided. Heinrich lost and for a while ended up in Normandy, acting as diplomat and ambassador for his father-in-law. One can imagine the imperial court getting a little tense when Heinrich came back with diplomatic papers. Heinrich ended up outliving Frederick, then defeating Frederick’s son in battle and retiring to Braunschweig where, to the surprise of everyone, he died of old age.
Heinrich wasn’t the only noble to collide with the emperor. But most others don’t have summer pageants dedicated to the fight. Given Frederick Barbarossa’s personality, and the times he lived in, someone probably would have poked him the wrong way. Rudolph “the Founder” von Habsburg would butt heads with several people, and would resort to dirty tricks to defeat the prince of Bohemia. (Dirty tricks meaning having a rested reserve launch, surround, and beat up on the Bohemians. That was frowned upon by the rules of chivalry. Rudolph was a pragmatist, and a survivor, and didn’t really care.)
First among equals, sword of the Church (sometimes), keeper of order, settler of disputes, and feudal overlord of the lands north of the Alps. The Holy Roman Emperors walked a bit of a tightrope, and it’s probably more surprising that they didn’t have more, greater conflicts with the other men of the empire.
* Parts of Poland remained pagan, or kept lapsing back into paganism, until at least the late 1100s. Then the union with (pagan at first) Lithuania distracted the missionary priests.
**If you are thinking “Welf sounds like Guelph as in Guelphs and Ghibillines in Italy, Dante’s mess” you are correct. In English, we used to say “Staufen” for the family, but the Germans started moving toward “Staufer” for the larger group and “Staufen” for one later branch, as in “von Hohen-Staufen.” English-writers have picked up that usage.