General Terms:
* Empire: This is the most common and widely recognized term. An empire is a large political unit, usually encompassing multiple kingdoms or territories, ruled by a single sovereign. The ruler may be an emperor, king, or other powerful figure.
* Hegemony: This refers to the dominance of one state over others, often through military power or economic influence. While not necessarily implying formal political control over the entire region, a hegemon wields significant sway over other kingdoms.
* Confederation: This is a political union of states, often formed for mutual defense or economic cooperation. While the member states retain their own autonomy, they agree to a central authority, which may have a powerful leader.
* Superpower: This term refers to a state with a significant amount of political, economic, and military power, allowing it to influence global affairs and exert influence over other nations. This could include kingdoms, although it's not a direct synonym.
Specific Terms:
* Imperium: This is the Latin term for "empire" and often used to denote a particularly powerful and encompassing empire.
* Universal Monarchy: This term refers to a single ruler who claims dominion over all known lands, often with a religious or divine mandate.
* Synarchy: This refers to a system of government where two or more rulers share power, often with one figure holding greater authority.
* Absolute Monarchy: This term describes a form of government where the monarch holds absolute power, ruling without any limitations or constraints.
Examples:
* The Roman Empire: A classic example of an empire, encompassing numerous kingdoms and territories under the rule of emperors.
* The Mongol Empire: An expansive empire that stretched across Asia, uniting different kingdoms and cultures under the rule of Genghis Khan and his successors.
* The British Empire: A global empire that spanned across continents, uniting colonies and dominions under the British Crown.
* The Holy Roman Empire: A complex entity that claimed the title of "universal monarchy," though its power fluctuated over time.
The specific term that best applies to a collection of kingdoms under one ruler will depend on the specific historical or fictional context and the nature of the relationship between the ruler and the constituent kingdoms.