the Wilhelminer War, Arnulf supported him and accepted his and his brother's homage. This ruined Arnulf's relationship with his uncle, Emperor Charles the Fat, and put him at war with Svatopluk of Moravia. Pannonia was invaded, but Arnulf refused to give up the young Wilhelminers. Arnulf did not make peace with Svatopluk until late 885, by which time the Moravian ruler was loyal to the emperor. Some scholars see this war as destroying Arnulf's hopes of succeeding Charles the Fat. King of East Francia Arnulf took the leading role in the deposition of Charles the Fat. With the support of the Frankish nobles, Arnulf called a Diet at Tribur and deposed Charles in November 887, under threat of military action. Charles peacefully agreed to this involuntary retirement, but not without first chastising his nephew for his treachery and asking for a few royal villas in Swabia on which to live out his final months, which Arnulf granted him. Arnulf, having distinguished himself in the war against the Slavs, was then elected king by the nobles of East Francia (only the eastern realm, though Charles had ruled the whole of the Frankish Empire). West Francia, the Kingdom of Burgundy, and the Kingdom of Italy elected their own kings from the Carolingian family. Like all early Germanic rulers, he was heavily involved in ecclesiastical disputes. In 895, at the Diet of Tribur, he presided over a dispute between the Episcopal sees of Bremen, Hamburg and Cologne over jurisdictional authority, which saw Bremen and Hamburg remain a combined see, independent of the see of Cologne. Arnulf was a fighter, not a negotiator. In 890 he was successfully battling Slavs in Pannonia. In early/mid-891, Vikings invaded Lotharingia and crushed an East Frankish army at Maastricht. Terms such as "Vikings", "Danes", "Northmen" and "Norwegians" have been used loosely and interchangeably to describe these invaders. In September 891, Arnulf repelled the Vikings and essentially ended their attacks on that front. The Annales Fuldenses report that there were so many dead Northmen that their bodies blocked the run of the river. After this victory Arnulf built a castle on an island in the Dijle river. Intervention in West Francia Arnulf took advantage of the problems in West Francia after the death of Charles the Fat to secure the territory of Lotharingia, which he converted into a kingdom for his son Zwentibold. In 889 Arnulf supported the claim