You are way way way oversimplifying nearly 1000 years of history between the plague of Justinian and the fall of Constantinople. The Justinian expansion was un

You are way way way oversimplifying nearly 1000 years of history between the plague of Justinian and the fall of Constantinople. The Justinian expansion was untenable. If you look at it on the map - there are strong enemies on literally all sides. It was a desperate but hopeless attempt to regain the Western Empire. The plague made it worse - but was hardly the catalyst. ...and the East Roman Empire was far more than a city state for a majority of the remaining NINE centuries.