The unification of the upper and lower kingdom occurred in the 'Protodynastic Period' of Egypt. There are many different sources that provide evidence how the unification occurred, such as the Narmer palette which originally led historians to believe that Narmer was responsible for the unification of the two halves of Egypt, however it is likely that due to trading and other factors such as the ability to write, and the power of the economy in the Naqada III period (3200 - 3000BCE), that the formation of a single Egyptian state occurred culturally beforehand.
The ability to read and write, which the Egyptian people gained in the Naqada III period, likely allowed trading to become much more profitable, as people could have definite records of inventory and money. The countries economy could also be improved by the ability to write. The use by both halves of Egypt of hieroglyphics contributed to the two halves developing similar cultures. The economic, military and political power of the state and the ideology of sacred power (which existed all throughout Egypt) would have contributed to a social setting where the unification was possible.
Discoveries at Hierakonpolis provided further evidence that the unification took place before Narmer, who the Narmer palette would have you believe unified Egypt by defeating his enemies, was pharaoh. Food production is found to have occurred, as pits at Hierakonpolis contained tens of thousands of domestic livestock bones, as well an array of wild animal bones. If this were to be a food production centre, then it would explain the power that Narmer (and many others after him), inherited. Due to the ability to control a population by controlling food production in an area, Narmer would have been able to control food in both the upper and Lower Egypt. This would mean that food would be centralized, giving the pharaoh control even before the unification. The pharaoh would have been able to view food production