Not sure if this is the right place to ask this, but I'll give it a shot.

Much of our understanding of historical empires comes from written records. So, how do we know that huge, Persia-sized empires didn't exist in prehistory? For the thousands—actually, tens of thousands of years before history, there's an enormous trove of archaeological, linguistic, and genetic information about human mass migrations. One late example is the Indo-European migration. Usually, these are explained as simple diffusion and not imperial conquest, but in the absence of writing, how can we know for sure that we're right?

My first thought was that "empires can't exist without writing", but apparently there are many counterexamples to this. One is the Inca Empire. It had other methods of record-keeping, so it didn't need writing. If we didn't have contemporaneous written records from the Spanish, I suspect there would be debate about whether the Incas really had an empire; many would just say they underwent a minor migration. Were there Inca-style empires anywhere in the world before the introduction of writing in Mesopotamia?