The answer lies not in The System, but in the cohesion of the spirit of the people; in a word the religion. Religion kept the AEs cohesive - and the religion was headed by a god and priest-magicians.
It was a religion based-upon magic: magic that worked.
How do we know Egyptian magic worked? 3,000 years - and the surviving artifacts, which are of a greater scope, finish and precision than was again attained until the Renaissance.
Ancient Egyptian technology is literally incredible by mainstream historical understanding - therefore a vital explanatory factor is missing. And that factor (since there is no survival of technologies that could plausibly have made the artifacts) was presumably magic.
Even the Old Testament acknowledges that there was real magic:
Exodus 7:
8 And the Lord spake unto Moses and unto Aaron, saying,
9 When Pharaoh shall speak unto you, saying, Shew a miracle for you: then thou shalt say unto Aaron, Take thy rod, and cast it before Pharaoh, and it shall become a serpent.
10 And Moses and Aaron went in unto Pharaoh, and they did so as the Lord had commanded: and Aaron cast down his rod before Pharaoh, and before his servants, and it became a serpent.
11 Then Pharaoh also called the wise men and the sorcerers: now the magicians of Egypt, they also did in like manner with their enchantments.
12 For they cast down every man his rod, and they became serpents: but Aaron's rod swallowed up their rods.
The account in Exodus takes it for granted that the Egyptian priests could do magic, and turn their 'staffs' into serpents - the difference between Aaron and the priests was that Aaron's rod made a more powerful serpent that consumed the others.
In other words; the Egyptian civilisation could only survive three millennia because it was (overall) reality based; therefore its essential knowledge claims were essentially correct: Pharaoh was a god (or demi-god), the Egyptian gods were real, and their priests really were magicians.
The account of Aaron's rod tells us that all these were subordinate to the One God, the creator and Father of the Hebrews - and the Ancient Egyptians knew that fact only implicitly and imperfectly; yet they knew a great deal about ultimate spiritual realities, and apparently fulfilled their destiny with great integrity.
