Ancient Egypt had a clearly defined historical chronology starting from 664 B.C.
In the third century B.C., Manetho divided Egyptian history from the great unification under Menes to the conquest by Macedon's Alexander into thirty dynasties, upon which later historians further subdivided Ancient Egyptian history into nine periods.
The first was the Predynastic Period, around 4000 to 3100 B.C.
The second was the Early Dynastic Period, around 3100–2686 B.C., which included the first and second dynasties and saw the rise of Menes, the first Pharaoh to unify Upper and Lower Egypt.
Of course, this is the most widely accepted speculation. History is too ancient, and there is not enough documentary history to prove that Menes was the first Pharaoh to unify Upper and Lower Egypt. In the study of Egyptian history, Narmer, Aha, and Scorpion King all have the potential to be the first unifier of Upper and Lower Egypt.