the northernmost of the three divisions, Lotharingia, was disputed between the kings of East and West Francia. The war over Lotharingia lasted until 925. Lothair II of Lotharingia died in 869 and the 870 Treaty of Meerssen divided his kingdom between East and West Francia, but the West Frankish sovereigns relinquished their rightful portion to East Francia by the Treaty of Ribemont in 880. Ribemont determined the border between France and Germany until the fourteenth century. The Lotharingian nobility tried to preserve their independence of East or West Frankish rule by switching allegiance at will with the death of king Louis the Child in 911, but in 925 Lotharingia was finally ceded to East Francia by Rudolph of West Francia and it thereafter formed the Duchy of Lorraine within the East Frankish kingdom. Louis the German was known at the time as "Rex Germaniae" (King of Germany) as his brother was called King of Gaul. This was meant to distinguish the different parts of a theoretically single Frankish kingdom, although it is not known if this was meant to signify anything further. East Francia was itself divided into three parts at the death of Louis the German (875). Traditionally referred to as "Saxony", "Bavaria", and "Swabia" (or "Alemannia"), these kingdoms were ruled by the three sons of Louis in cooperation and were reunited by Charles the Fat in 882. Regional differences existed between the peoples of the different regions of the kingdom and each region could be readily described by contemporaries as a regnum, though each was certainly not a kingdom of its own. The common Germanic language and the tradition of common rule dating to 843 preserved political ties between the different regna and prevented the kingdom from coming apart after the death of Charles the Fat. The work of Louis the German to maintain his kingdom and give it a strong royal government also went a long way to creating an East Frankish (i.e. German) state. Stem duchies Within East Francia were large duchies, sometimes called kingdoms (regna) after their former status, which had a certain level of internal solidarity. Early among these were Saxony and Bavaria, which had been conquered by Charlemagne. In German historiography they are called the jüngere Stammesherzogtümer, or "younger stem duchies", The conventional five "younger stem duchies" of the Holy Roman Empire are Saxony, Bavaria, Franconia, Swabia and Lotharingia. Thuringia, while one of