Your challenge: Divide at least 90% of the global population at some point in human history between five or fewer "world empires", such that the "smallest" empire has at least twice the population of the remaining humanity.* Bonus points if the five governments get along well enough for their emperors or government leaders to meet on a regular basis, or at least have representatives to do so (like a quasi-UN).
*So, for example, if you have five such powers, the fifth largest "realm" needs to be twice as populous as all humanity not living under any of said five.