Middle Francia
Louis III (the Younger) was a son of the East Frankish king Louis the German who divided the East Frankish realm among his sons in 865. Louis the Younger got the biggest part of East Francia, his brothers got Bavaria and Northern Italy. In the Treaty of Meersen he additionally gained the eastern part of Middle Francia. Charles the Bald, king of West Francia, tried to occupy whole Middle Francia before and only agreed to the treaty due to military pressure. After Louis the German died Charles again tried to extend West Francia to the east until the river Rhine. To achieve that he met his nephew Louis the Younger in Sinzig, but Louis didn't agree to Charles' plans.