Vassalage is a system in which one political entity, known as a vassal, pledges loyalty and service to a more powerful entity, known as a suzerain or overlord. In the context of the question, the Hausa-Fulani practiced vassalage as a political system.

Historically, the Fulani established various states and emirates across West Africa. In these states, vassalage was often a political arrangement where smaller entities or groups pledged allegiance to the Fulani rulers, offering loyalty, tribute, and military support in exchange for protection and certain privileges. The Fulani-led Sokoto Caliphate, established in the early 19th century in what is now northern Nigeria, is an example of a political entity where vassalage played a role. The Fulani leaders held sway over a diverse range of ethnic groups and communities, and vassalage was a mechanism through which they maintained control and ensured the loyalty of different regions within their caliphate.