WI: Frankish Iberia

You may be able to get a Frankish Iberia, but not in the way you describe in the OP. It would have to involve a more violent entrance into the Roman Empire methinks rather than the more peaceful and cooperative settlement they reached IOTL. So something more like the 406 invaders, where they kept on moving until they stormed into Iberia.
 
I mean the Franks annex Iberia to their Empire creating an empire stretching from Germania to Iberia.

Not likely, unless you prevent the Umayyad invasion and make Visigoths to last more and decline harder.

Franks and Visigoths were enemies and for a long time the former were Catholic and the later were Arian. Franks at their first peak of power in the 5th century only managed to expell the Visigoths from Aquitaine but they never managed to take Septimania, which lies North of the Pyrenees. So the whole Iberia was too much challenging.

And then the Franks suffered divisions (Neustria vs Austrasia) and much infight to be capable of that. When Franks unified and started to rise again by the 700s, the Umayyads invaded Spain. Maybe if the Umayyad invasion would have not happened, the Franks could have took Spain by the late 700s - early 800s with Charlemagne and co.
 
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