After the collapse of the Western Roman Empire, and the occupation of Gaul by the Franks, Roman power never returned far enough to come into conflict with the Frankish kingdom. The Franks instead soon became the predominant power in Western Europe. By 774, the Franks were, together with the eastern Roman Empire, the only organized Christian kingdoms.
Indeed, to many countries the Franks became Western Europe, as the words for “European” in Arabic, ifranji, and Persian, farangi, still show.
The original core of Francia, the Frankish Kingdom that came to dominate the West under Charlemagne, can be identified as those areas upon whose ruler the Pope at one time or another conferred a crown as the Roman Emperor. Charlemagne himself ruled modern France, northern Italy, and most of modern Germany. After the death of Charles the Fat in 888, the imperial title was conferred to the Kings of Italy, and then lapsed entirely in 922.
The “Empire” came to be regarded as consisting of four crowns: (1) East Francia, or Germany, (2) Lombardy (the “Iron Crown”), or Italy, (3) Rome, and, after 1032, (4) Burgundy. Lorraine, which had been a separate kingdom in the inheritance of Charlemagne, soon become part of the system of “Stem Duchies” in Germany.
Most of those Stem Duchies, like Saxony, Franconia, and Bavaria, corresponded to preexisting German tribes.
The marches were border territories that involved a great deal of fighting. In Charlemagne’s day, that included marches in Spain contesting the Islâmic advance. Later, the German marches north and south of Bohemia extended German settlement far to the east. Brandenburg became the most famous northern march, remaining a margravate until becoming the Kingdom of Prussia. Austria (Österreich, the “eastern realm”) was the most famous southern march, becoming a duchy, then the only “archduchy,” and finally an empire.
As the authority of the German Emperors declined, and that of the Kings of France grew, the “Middle Kingdom” (Francia Media) of Lorraine, Burgundy, and Italy began to pass either from German to French control (Upper Lorraine, Burgundy) or from German control to separate status (Lower Lorraine, i.e. the Netherlands and Belgium, and Italy). This process continued well into the modern period, when we see a multiplication of kingdoms, reaching five in Germany (not counting Bohemia) and two in Lower Lorraine. The Dukes of Savoy, beginning with a county in Burgundy, acquired more land and a capital (Turin) in Italy, named their new Kingdom after Sardinia and ultimately succeeded as the modern Kings of Italy.