When the various Germanic tribes found that they could settle on the lands once occupied by the Romans and their vassals, they were elated. Before the highly symbolic victory of Alaric, wandering tribesmen were in danger of being slaughtered by Roman border garrisons should they find themselves inextricably deep into Roman territory and without hope of withdrawal and retreat.
With the increasing incursions of the Huns into German lands, and the panic this caused, the tribes became ever more incautious, and in some cases the ancient councils decided on uprooting and migrating into Roman franchises defended by Roman forces, with all the risks that entailed.
The so-called Visigoths, or Western Goths were among the first of the Germanic peoples to survive for a prolonged period of time within Roman borders. After being confronted with the reality of annihilation through some unrecorded massacre of their tribal brethren by Hunnic invaders, the Visigothic warriors hoisted Alaric on their shields, and decided to enter Italy.
The great Vandal general Stilichus was charged by the Roman Senate with pursuing and destroying Alaric and his army, however in a whirlwind of military strategy Alaric saved his people and his soldiers sacked Rome, before the group escaped to first Aquitania and then Iberia.
Similar stories were repeated elsewhere, until all the major parts of the Western Roman Empire hosted substantial Germanic populations, such as the Franks, the Burgundians, the Suebi, the Vandals and others. These quickly learned to speak the dialects that the locals had created from proper Latin, and called themselves Romans, as well.
There is no evidence that these new Romans, who might be Christians, had any idea of the pagan and sometimes hedonistic Roman Imperial life-style that had been the unchallenged norm before Emperor Constantine embraced Christianity. They grew increasingly conscious that the Catholic religion, as led by the Pope of Rome, was extremely important in their new lives on Roman lands, and those who still followed traditional religious beliefs, whether Christian or not, would be persuaded to embrace Catholicism wholeheartedly before long.
When these new Roman citizens first came together for battle against an enemy of Rome, and Mohammad had declared himself such at an early date, it was natural that they should style themselves as Holy Romans, rather that simply Roman.
The label stuck, and the entire Gallo-German-Roman culture became an intertwinement of religious and military duties, where some of the Imperial Roman institutions (titles and duties) were preserved in one form, or another, but other things were done strictly through the offices of the Church, the Bishops, Priests and other Clerics.
In some senses the entire Holy Roman establishment was more unified, not less, than the Roman Empire that preceded it. This was because Clerics could keep accurate marriage records of the noble landowners, and advise marriages based upon these records, strengthening ties between the ruling families. It was even said on some occasion or other that all the nobles of Europe were related to Jesus Christ to some degree. Holding such a belief in these days might entitle you to an extended stay in a mental institution, and imitation of the religious fervor and depth of belief of those times is generally discouraged, much as would have had the “enlightened” instructors in the ages that followed.
Both the ancient Roman families and the Germanic newcomers were more or less satisfied with this system, which allowed some of the old Romans an excessive amount of influence in the distribution of entitlements through their long residency in the city of Rome, itself, while giving the Germanic settlers a chance to work the land and prove themselves through service to their feudal overlords, whether they be Roman or German.
The Medieval Age and the Holy Roman Empire are denigrated by the thinkers, or philosophers of the Enlightenment as “Dark Ages,” but they were as much a part of European History as the Renaissance and the Age of Discovery and might have been a fortunate way that the newcomers from the North were spared immersion in the greatest excesses of the pagan Roman world, including the gratuitous violence and blood-sport of the gladiatorial arenas, the prostitution of slaves and servants, as well as other exploitative and abusive practices known to have been ordinary business in the dark places and shadows of Ancient Rome, the Rome that existed as a pagan construct, replete with witches and their magic, gods and demi-gods and auguries of all sorts.