Why does China work in place of Ming and Han Dynasty but not in place of Qing (where China got its name, after all), Yuan or Tan? That threw me off. Also, the Ummayid Caliphate was larger than either the Abbasid or Rashidun Caliphates. You include the latter two but not the former. The American Empire is officially 9.8 million square kilometers currently, and much larger if you count all the countries in their sphere of influence that they control more directly than, say, the 95% of Brazil that the Portuguese claimed as part of their empire but never directly controlled.