Oh well then It'd be conquest or in other words, force
The planting of crops in the beginnings of human society resulted in economic stability.
At this time the capitol of Upper Egypt was known a Nekhen while the capitol of Lower Egypt was Nekheb later called Heiroconopolis (the falcon city).
After many years of warfare it was the warrior-king Menes (c3000BCE) whose armies finally defeated the armies of the southern nomes or city states, that are collectively known to us as Upper Egypt.
hope this helps
