Doesn't seem true to me; people seem aware of the Mayans and some of the stuff going on in Asia at the time (though generally not all).
It's an extra bummer quite simply because civilizations in the middle interact with more civilizations, and so are a great way to tie together everything else one remembers into a coherent whole.
(Umayyads conquer Sassanids and 100-200 years later have a big only-old-school-military-historicans-think-it-matters one-off battle with the Tang dynasty in like modern Tajikistan or something. What a great flashcard!)
Really? The Romans are known for their expansionism. Who were they conquering? Who was everybody fighting against in 300?
There was plenty of interaction, but the thing about those insignificant barbaric tribes is that they aren't worth conquering either.
The Macedonian empire was technically larger, including Persia, except it was never administrated as a whole and fell into pieces just a few years after coming into existence.
(This was, in fairness, largely how the Romans represented it to themselves, regardless of how true it was, so it's maybe not surprising.)
> hinges on the current fad of 'Europeans are all racists and didn't appreciate a Black civilization', which is of course wrong.
... eh, until last century it was fashionable to attribute it to "just an Egypt copy, basically".
EDIT: On the latter topic, RE the guy who looted the Sudanese pyramids:
> He tried to sell the treasure, but at this time nobody believed that such high quality jewellery could be made in Sub-Saharan Africa.
The stuff he stole ultimately ended up in two German museums for _Egyptian_ artifacts.