What is An Empire

A complex political organization where a dominant central state controls weaker outer states

No, Egypt was a kingdom because all of it's citizen in the surrounding cities identified as Egyptians.

In empires, citizens identify with their own city/region/state

There is no single reason, however, one state decides it wants power and control over the others.

The two most popular reasons they exist are to conquer other states for resources as well as security and wealth

It's based on inequality (core vs peripheral)

The core idetifies itself as superior over it's periphery

No prior examples (trial and error)

Overextension is difficult