Louis the Younger had inherited Bavaria, Charles the Fat had been given the Kingdom of Italy and Arnulf had been confirmed in Carinthia by an agreement with Carloman after the latter had been incapacitated by a stroke in 879.
Bavaria, however, is ruled more or less by Arnulf.
Arnulf had in fact ruled Bavaria during the summer and autumn of 879 while his father arranged his succession and he himself had been granted "Pannonia," in the words of the Annales Fuldenses, or "Carantanum," in the words of Regino of Prüm.
The division of the realm had been confirmed in 880 on Carloman’s death.
When, in 882, Engelschalk II rebelled against the Margrave of Pannonia, Aribo, and ignited the so-called Wilhelminer War, Arnulf had supported him and even accepted his and his brother's homage.
This has ruined Arnulf's relationship with his uncle the Emperor and put him at war with Svatopluk of Moravia.
At first, the rebels were successful, until Aribo appeals to not only Moravia, but also the Emperor Charles the Fat, who confirms Aribo in his post, to which he had been appointed by Charles' father, Louis the German, back in 871.
Svatopluk invades Pannonia and, capturing one of the Wilhelminer brothers, mutilates him.
The remaining sons then withdraw from Charles' suzerainty and do homage to Charles' bastard nephew, who thus estranges himself from his uncle.
The war between Arnulf and Svatopluk escalates after the former refuses the latter’s request to to surrender the Wilhelminers.
