Treaty of Verdun and the Division of the Frankish Empire
Also called: Treaty of Meerssen
In 843 Charlemagne’s three grandsons divided the Frankish empire into East, West and Middle Francia by the Treaty of Verdun, and in 870 the Treaty of Meerssen divided the north of Middle Francia again.

Great Politburo · CC BY-SA 4.0 · Source
The Franks customarily divided land equally among their sons. After the death of Charlemagne’s son Louis the Pious, his three sons fought and in 843 made the Treaty of Verdun, splitting the empire in three. The eldest, Lothair, took the imperial title and Middle Francia, stretching from Italy to the North Sea; Louis took East Francia and Charles took West Francia.
When Lothair’s line died out, the Treaty of Meerssen in 870 divided the lands of Middle Francia north of the Alps between East and West Francia. East Francia, West Francia and Italy, as thus divided, became the origins of today’s Germany, France and Italy. At the same time in Silla, Jang Bogo was leading maritime trade from his base at Cheonghaejin.