Term limits.
Since the subject is the end of an African king’s reign…
I recall reading an account of royal investiture ceremonies in tribal Africa where the incoming monarch was presented a bowl of pebbles. Plunging his hand in, he seized a handful. The harvest was then counted and announced with each pebble representing a year of his upcoming reign. The implication being that, if he had not already died, measures would be taken (poisoning, IIRC) to remove him after his final year ended.
I imagine there was considerable discussion about how large (or small) the pebbles in the bowl should be…