Received the northern part of his father's domain, known as Lotharii or Hlutharii Regnum, corrupted later into Lotharingia or Lorraine.
843 the Rhine formed the boundary between Germany and the middle kingdom of Lotharingia; but by 870 it lay wholly within the former realm.
Rather than acknowledge him, the duke of Lotharingia-, or Lorraine, transferred his allegiance to Charles the Simple of France; and it was in vain that Conrad protested and despatched armies into Lorraine.
In 843, by the treaty of Verdun, it became part of Lotharingia (Lorraine), and in 879 was annexed to the kingdom of East Francia (Germany) by the treaty of Meerssen.
However, asthe boundary between the possessions of Charles the Bald and those of Louis was not strictly defined, and as Lothairs kingdom, having no national basis, soon disintegrated into the kingdoms of Italy, Burgundy and Arles, in Lotharingia, this great undefined territory was to serve as a tilting-ground for France and Germany on the very morrow of the treaty of Verdun and for ten centuries after.
Since he could not dismember the kingdom of France, his only course was to reconstitute the ancient kingdom of Lotharingia; while the conquest of the principality of Liege and of the duchy of Gelderland, and the temporary occupation of Alsace, pledged to him by Sigismund of Austria, made him greedy for Germany.
At the partition treaty of Verdun (843) Frisia became part of Lotharingia or Lorraine; at the treaty of Mersen (870) it was divided between the kingdoms of the East Franks (Austrasia) and the West Franks (Westrasia); in 880 the whole country was united to Austrasia; in 911 it fell under the dominion of Charles the Simple, king of the West Franks, but the districts of East Frisia asserted their independence and for a long time governed themselves after a very simple democratic fashion.
After the partition of the territory of Charlemagne's empire among the sons of Louis the Pious, Walcheren and the Scheldt-mouth fell within the possessions of the emperor Lothair, and in the region subsequently distinguished as Lotharingia.
On the division of the Carolingian realm the part of the province to the east of the river fell to the share of Germany, while that to the west remained with the evanescent kingdom of Lotharingia.
Already, in 926, they had crossed the Rhine and ravaged Lotharingia.