There is no set way to achieve this other than the objective is to defeat all other factions. The best way to avoid this is to keep good relations with Lords or capture the kings and lords before taking the last castle/town. *This achievement can be a little glitchy, as you can control every town and village in the game but have a non-surrendering king who will completely disappear from the game until one of their vassals conquer a town/village. Empress can be achieved with either The Golden Throne or Manifest Destiny Just ensure you choose to play as a female when setting up the character.
