Final answer:
The Roman Empire was divided up in three with the system of tetrarchy, which divided the empire between four rulers and into two halves: east and west. However, this system often failed and eventually the Emperor Constantine became the single ruler of a united Roman Empire.
Step-by-step explanation:
The major empire in world history that was divided up in three is the Roman Empire. During the third through fifth centuries, the Roman Empire underwent massive changes and was divided between four rulers and into two halves: east and west, in a system known as the tetrarchy. However, after the death of Emperor Diocletian, this system often failed and eventually the Emperor Constantine emerged as the single ruler of a united Roman Empire.