From 882 to 884, the Wilhelminer War engulfed the March of Pannonia (later March of Austria). Arnulf of Carinthia, Charles's illegitimate nephew, made an alliance with the rebel Engelschalk II against Aribo of Austria, Charles' appointed margrave of the region. Svatopluk I, ruler of Great Moravia, agreed to help Aribo and in 884 at Kaumberg took an oath of fidelity to Charles. Though the emperor lost his vassals of the Wilhelminer family and his relationship with his nephew was broken, he gained powerful new allies in the Moravian "dux" and other Slavic "duces" of the region.