By his time of the Hyksos the middle kingdom no longer was named as an honorary part of Mizraim, even though it did not exist. The Two Kingdoms were named instead.
After the word "kemi" for river-borne silt, the whole region was often called the Land of Kem. From the color of red desert surrounding the black-silted river valley, the region got another popular name, the Land of Red and Black.
Upper Mizraim was also called the White Kingdom, Lower Mizraim was known as the Red Kingdom, after the white and red crowns wore by the respective kingdom's rulers. (On Earth, Mizraim was later called "Egypt" after the Coptic people who formed the original population during the Roman era and afterwards. This name did not take firm hold on Earth II, however, for the traditional name, Mizraim, survived into the modern eras).
The population at its height was about four or five million, but these were for much of Mizraim's earlier history well-fed and relatively well-housed in a hot climate requiring no heating of buildings. Having no comparison, this society assumed it was the center of the Universe and nearly proved it.