From 602 to 628 the Byzantines and Sassanids were fighting what is called the the “Last Great War of Antiquity”.

It was the final and most destructive war between the Romans and Persians, which ended in a Byzantine victory, but destroyed each empires army and had destroyed their economies.

This left a power vacuum that the Arabs united by Islam exploited and conquered the Persians and a lot of the Byzantine empire in the middle east.

Officially ending the dominance that Rome and Persia had for over a thousand years, thus ending the ancient age and starting the dark ages.