https://www.thecollector.com/justinian-plague-affect-byzantine-army/
Bit harsh blaming Justinian
He should definitely have washed his hands before leaving the latrina...
Silly boy :P
I'm not at all sure that the Justinianic plague was quite as devastating as the blogger thinks. It did not cripple the military potential of tge Empire. In 552 Narses was able to pick up an army recruited by Germanus and launch an attack on the Ostrogothic kingdom which was very likely at least 1.5 times , maybe twice as large as the Gothic army. In the same year IIRC Justinian launched an attack upon Spain, taking over lands that were claimed by the Visigoths , althoughhthey might have been more the territories of Roman cities . I cannot recall any point at which the chroniclers claim that this or that army was so reduced by plague as to be unable to perform.
The idea that the plague was a major factor in the failure of the Romans and Sassanids to beat off the attacks again sounds to be a bit if a stretch. The Empires look to have little problem in producing troops for the Arabs to beat and we would be guessing to suggest that somehow tge better troops had suffered from the pandemic some eighty years before. Arab tactics and command are a better solution.