Isaiah's intention was perhaps not so much to point to one particular time in history, but rather to show how a nation is affected when it is judged by God. He uses the first person to emphasize that it is the Lord speaking. The result of the judgment would be civil war—Egypt turning on itself. That being said, historical sources do indicate times when Egypt was divided into many smaller kingdoms.
2 And I will stir up Egyptians against Egyptians, and they will fight, each against another and each against his neighbor, city against city, kingdom against kingdom;