In cryptic-crossword clues, “of the French” is usually translated as the sequence DU or DES, since the French words du and des can both be translated as “of the” — the former in reference to a singular masculine noun, the latter to a plural of either gender. For singular feminine it would be de la, but I don’t recall ever seeing DELA so clued.
I don’t mean to write about crosswords, however, but about the fact that for a year or so (1791-92) following the French Revolution, when France was a constitutional monarchy, Louis XVI’s title was changed under Constitution of 1791 from King of France and Navarre (Roi de France et de Navarre) to King of the French (Roi des Français). The same style was adopted later by Louis-Philippe (1830–1848), and an analogous one (Emperor of the French) by both Napoleons. Only under the Bourbon Restoration (1815–1830) was the old style revived.
Moreover, every time that France has been governed as a republic it has been as République Française (French Republic), not, say, République de France. It seems as if the use of the demonym rather than the toponym made the regime seem less autocratic and more “popular.” But, as the royalist historian Guy Augé has pointed out, the change to Roi des Françcais was a “curious and unconscious return to the expressions of Medieval Latin.” In fact, the Old French Rei des Franceis was a meant as a literal translation of Rex Francorum, a title that had been used continuously until about 1190 and intermittently — alternating with Rex Franciae — thereafter. I have found only one instance of Rei des Franceis in an official document; it dates from 1266, a time when such documents in anything but Latin were extremely rare.
Rex Francorum (King of the Franks) was originally a tribal title, first used in the 5th century by Clovis I, at a time when Germanic warrior tribes moved around Europe and their rulers governed whatever territory they happened to conquer. Clovis ruled over much of what is now France (the French consider him to be their first king), but divided his kingdom among four sons, every of whom was also called Rex Francorum, and so it went on for the next several centuries when the kingdom was repeatedly reunified and redivided.
The Franks, like the other Germanic peoples who invaded various parts of the Roman Empire, came to constitute a warrior caste that governed their territory, and Rex Francorum meant, essentially, something like warrior in chief. The territory that they ruled came to be called Francia. In the 9th century, under Charlemagne, a distinction began to be made between western (Occidentalis) and eastern (Orientalis) Francia, the latter being the land inhabited mainly by Germans. The division became official at the Treaty of Verdun (843), in which a middle kingdom (Francia Media) was also created, but this soon thereafter became known as Lotharingia. During most of the 9th century several of the Frankish kings (east and west) also held the title of Roman Emperor, which was the primary title they used, and those who didn’t usually called themselves simply Rex so as not to limit the extent of their reign, in contrast with the fact that in reality their actual rule did not extend beyond their immediate fiefs while their vassal dukes and counts became more and more independent.
In the 10th century the imperial title became a monopoly of the Eastern kings, who stopped using any reference to the Franks; the first of these emperor-kings, Otto I, was not a Frank but a Saxon. Now only the Western kings, beginning with Charles the Simple, used the title Rex Francorum, and by the 11th the term Franci (Franks) lost its ethnic significance and came to mean all those who were vassals of those kings, if only in name. Normandy and Catalonia, for example, were at the time a virtually independent duchy and principality, respectively. The former’s dukes were, of course, ethnic Norsemen, and the latter’s princes — known as Counts of Barcelona — were of Visigoth descent. Nevertheless, in the Bayeux Tapestry the Normans conquering England are called Franci, and in the Poem of El Cid francos refer to Catalans.
By the 11th century the name Francia, previously confined to Latin documents, passed into the vernacular as France. Before that, France had another meaning. In the 9th century the counts of Paris were also called Duke of the Franks (Dux Francorum), and the territory of which they were overlords — Paris and some counties surrounding it — was also called Francia. It is much more likely that a term will be adopted into the vernacular if it corresponds to everyday experience, and the denizens of this region came to call it France, alongside the demonym franceis (modern Français), to contrast it with neighboring regions such as Normandy and Champagne; the larger Francia was not of much importance to ordinary people. This usage survives in place names, such as Roissy-en-France (the home of Charles de Gaulle airport) as distinct from another Roissy which is in the old county of Meaux, at the time a fief of the counts of Champagne, and in the division of geographic formations such Vexin to the west into Vexin français and Vexin normand, and Brie to the east into Brie française and Brie champenoise. But in the 11th century Franceis came to be the French equivalent of the Latin Francus, and was used retroactively in the Song of Roland, interchangeably with Francs, to refer to Charlemagne’s Franks fighting in Spain.
Note, however, that all these references to Franks or Franceis are to fighting men, from knights to dukes, and not to commoners. The title Rex Francorum (or Rei des Franceis) continued to carry the meaning of leader of the warrior caste, not of the common people. The change to Roi de France meant that the king ruled over all the people of his territory, including the increasingly important merchant and artisan classes of the cities, which struggled with the crown for autonomy throughout the later Middle Ages. This is just the opposite of what the French revolutionaries thought.