What are some underrated points of divergence during the fall of the Roman Empire and early "Dark Ages", especially from 313 AD to 565 AD?
Dun-Dun-DUUUUUUUN
Battles
- Battle of Argentoratum (357), which opposed Romans and Alemanni. Julian being defeated would have meant Gaul being less safe it was during the IVth, at least for the decade, pulling strategical changes in western Romania which would have made the situation managable, but at the cost of some sacrifices (maybe an earlier gradual pull-out of Britain?)
- Battle of Ctesiphon (363), opposing Sassanians and Romans. It could go two ways : either clear Roman victory with Julian surviving, either clear Sassanian victory. Both ways would have important macro-historical situations.
- Battle of Solicinium (368) which opposed Romans and Alemanni. It had potential to be a western Adrianople, meaning less big immediate changes, than the possibility for an Alemanic build-up in the region, where a leader could pull an Alaric.
- Battle of the Frigidius (395), which opposed Theodosius to Eugenius. The battle wasn't that well engaged by Theodosius, whom Gothic federates went trough severe losses. It litterally didn't asked for much more than a turning wind to provide Eugenius and Abrogast an advantage. A Theodosian defeat, and the victory of a pagan emperor and magister militiae, as well no career in the west for Stilicho would have massive consequences.
- Battle of Verona (402), which opposed Goths to Romans. The capture of Alaric would have certainly led to interesting change in the relationship with and between Goths. I'd expect some disbanding (while not much infra-structural weakening) leading to maybe a bit of respite for WRE.
- Battle of Obrigo (456), which opposed Goths to Suevi. A Gothic defeat, or rather a stalemate, may have provided Suevi enough base to hold their ground in Spain
- Battle of Deols (469) which opposed Visigoths to a coalition made of Britto-Romans, Gallo-Romans and Franks. It sealed Visigothic dominance in Gaul for decades, until Clovis' conquest.
@galileo-034 is working on it since ages, but I generally agree that it might involves (in the case of a visigothic defeat) a Burgondian success in southern Gaul, an easier and earlier Frankish progression, Armorican Saxons being more important and a general mess in Aquitaine.
Other
- A more successful Armenian revolt movement in the late IVth may have been more problematic for Sassanians for what matter campaiging in Anatolia, or at least would have provided yet another battleground with Romans.
- Survival of Balthi dynasty in Gothic Spain may have helped to prevent the anti-dynastical take on kingship that went institutionalized between the VIth and the VIIIth. Conversly, the disappearance of Merovingian dynasty early on would have interesting consequences as well.
- An earlty death of Brunhild might have shortened the faida that existed between the various Frankish kings.
- The absence or early defeat (naval, tough) of the Vandalic War in the 530's
would have in all probability led to a Maur takeover of post-imperial Africa
There's probably much more, but that's all I can think off on top of my head.