Their contract of 870 at Meerssen replaced the 843 Treaty of Verdun, after which the Carolingian Empire was also split into three parts, by dividing the northern half of Middle Francia stretching from the Rhone valley to the North Sea, in effect recombining sundered territories of Francia into two larger east and west divisions.

The empire of Louis the Pious, son of Charlemagne, had originally split in three parts by the 843 Treaty of Verdun: Lothair I, his eldest son, received the Imperial crown and the personal realm of Middle Francia Louis the German († 876), the second born son, received East Francia (which would evolve into the Kingdom of Germany) Charles the Bald († 877), his half-brother, received West Francia (which would evolve into the Kingdom of France), although this was disputed by Pepin II of Aquitaine until he was captured Upon the death of Lothair I in 855, his realm of Middle Francia was partitioned between his sons by the Treaty of Prüm: Louis II of Italy († 875), the eldest son, received the imperial crown and Italy Charles of Provence († 863) became King of Provence (Lower Burgundy and Provence proper), later partitioned by Louis II and Lothair II Lothair II († 869) received Austrasia (the central part still controlled by his father after Verdun), Frisia and Upper Burgundy – this realm came to be named Lotharii Regnum (Lotharingia) East Francia and West Francia remained as before: Louis the German († 876) ruled East Francia Charles the Bald († 877) ruled West Francia Lothair II ceded the southeastern parts of Upper Burgundy to his brothers, whereupon Charles of Provence received the bishoprics of Belley and Tarentaise in 858, and Louis II of Italy the bishoprics of Geneva, Lausanne and Sion the next year.

Lothair II received the western Lower Burgundian parts (bishoprics of Lyon, Vienne, Vivarais and Uzès) which were bordering his western Upper Burgundy (remnants of his original Burgundian possessions), while Louis II received the rest of the Kingdom of Provence.

In turn, after Charles the Bald had died and his successors struggled to consolidate their rule over West Francia, Louis the Younger campaigned in western Lotharingia in 879.

Charles's grandsons were forced to cede the whole of Lotharingia to him, sealed by the 880 Treaty of Ribemont, according to which it finally became part of East Francia.