The Treaty of Verdun (843) restores peace and divides the Carolingian empire among three sons, geographically and politically delineating the approximate future territories of Germany, France, and the area between them, known as the Middle Kingdom.

The eastern Carolingian kings rule the East Frankish Kingdom, what is now Germany and Austria; the western Carolingian kings rule the West Frankish Kingdom, what becomes France. The imperial title, however, comes to depend increasingly on rule over the Middle Kingdom.

By this time, in addition to a geographical and political delineation, a cultural and linguistic split has occurred.

The eastern Frankish tribes still speak Germanic dialects; the language of the western Frankish tribes, under the influence of Gallo-Latin, has developed into Old French.

Because of these linguistic differences, the Treaty of Verdun has to be written in two languages.