So, what if the Frankish kingdom of Austrasia survived the Frankish Empire's dissolution, eventually becoming the nucleus of an independent kingdom?
The Early Middle Ages are not an era I really am familiar with, but so far as I can tell the kingdom disappeared largely as a result of the various Frankish partitions. I suppose one way to accomplish this (aside from a different partition scheme) might be to nerf the Franks somewhat- say kill Charlemagne off during the Saxon wars and have Austrasia and Neustria go their separate ways thereafter.