Egypt has been a crossroads for humanity for millenia. The people who live there now are not the descendants of the people who built the great civilizations of the past. The ancient Egyptians of the pre-Alexander era, were most likely traders with the Phoenicians (Carthage, Spain, Tyre and Sidon) and may have hitched a ride with them to southwestern Europe when things got heated in the wars with Babylon, Assyria and eventually Greece and Rome. When they moved out, the Arabs moved in....................
Ah, but Egypt was NOT really just a crossroads, not in that way.
A “crossroads” would be an entrepot, of a relatively large number of people from elsewhere passing through, and sometimes settling. But such a population in ancient times was doomed to genetic death, as urban populations could not reproduce themselves. Thats why population geneticists call them “sinks”. Egypt had several entrepots. They never seem to have represented much of the general population. Egypt had Alexandria, but Egypt wasn’t Alexandria.
Egypt was a very heavily populated, intensively cultivated country, continuously so for thousands of years. It may have been the most populous of any country around the Mediterranean. Just its agricultural surplus (and surpluses were small per capita in those days) could feed most of Italy at various times.
At bad times the Egyptian population may have outnumbered everyone else for a thousand miles around.
There is no way an ancient invader could have out-bred or genetically co-opted this enormous mass of peasants. Plenty of people conquered the Egyptians, but I doubt anyone replaced them.