Very succinct, thank you. I mentioned Parthia because Axum was a contemporary of theirs, but they lasted for an insanely long time, so they were a contemporary of the Sassanids too.

And if I remember correctly, the Sassanids were a Satrap of Parthia who revolted and ended up taking most of their territory from them. And both the Sassanids and Eastern Romans spent so many resources fighting each other that the Muslims were able to devastate both empires. (though there's more too it than just that obviously)