empire vs sovereigndom

empire

noun
  • A political unit, typically having an extensive territory or comprising a number of territories or nations (especially one comprising one or more kingdoms) and ruled by a single supreme authority. 

  • An expansive and powerful enterprise under the control of one person or group. 

  • A political unit ruled by an emperor or empress. 

  • The group of states or other territories that owe allegiance to an imperial power (foreign to them), when distinguished from the native territory of that power; imperial possessions. 

  • control, dominion, sway. 

sovereigndom

noun
  • The state, condition, or realm of a sovereign; sovereignty. 

How often have the words empire and sovereigndom occurred in a corpus of books? (source: Google Ngram Viewer )