Answer:
German tribal states.
Step-by-step explanation:
(476 AD)
Due to the sabotage of German states and a higher official (Arminius) of the Roman empire back stabbing the king marked the decline of the empire, using gorilla warfare Arminius issued a note stating he needed help with taking down a rebellion. the king being close friends with Arminius sent a good majority of the Roman troop, when they got to the main road to that German city they then came out the bushes, most Roman troops where scared of German troops, so they then for ran away died or just got disorganized which then made the whole troop fail , having then German states would constantly go against the empire untill it collapsed.
As well as having a huge empire not having troops to cover it and having your Capital burned down by a new emperor caused it to fall into what's then going to be called the 2nd Roman empire (Byzantine)
(In 1290 AD)
the Byzantine empire would have there most turning revolt the ottoman empire would then kill the rest of the remaining empire in 1400 ad starting some where in 1290's.