A vassal king refers to a monarch who retains a certain level of sovereignty over their own kingdom or territory but is subordinate to a more powerful ruler or empire. This relationship is often formalized through treaties or oaths of loyalty, where the vassal king agrees to provide military support and tribute in exchange for protection and autonomy.
The concept of vassalage has its roots in the feudal system, which was prevalent in medieval Europe. In this system, a lord would grant land (or fiefs) to a vassal in exchange for loyalty and service. A vassal king operates on a similar principle; while they may maintain authority over their subjects, they ultimately owe allegiance to a higher authority, such as an empire or a sovereign king.
Historically, there have been many examples of vassal kings. For instance, during the height of the Mongol Empire, many regional rulers were allowed to govern their lands as vassal kings under the Mongol khans. They were expected to pay tribute and support the empire in military campaigns, yet they retained a degree of local power and autonomy.
In summary, a vassal king is a somewhat independent ruler who has pledged allegiance to a more dominant power, balancing loyalty and local governance with the obligations that come from being a vassal.