An empire refers to a large group of states (with a large population) that are concentrated under the power of a single authority. During Classical times, several empires arose, such as the Persian, the Roman and the Chinese Empire.
There are several lessons on tolerance and wise government that we can learn from these empires. For example, the Persian and the Roman Empire was tolerant with their newly-conquered peoples by allowing them to keep many of their traditions, laws and religions. The Roman Empire also exercised wise government by employing some unifying tools, such as common citizenship. Finally, the Chinese Empire exercised wise government by unifying all people under a common culture, but also improving the living conditions of the conquered people through engineering projects and access to education.