Берешит 10:6 Мидраш: Midrash Tanchuma, Ein Yaakov (Glick Edition), Mekhilta DeRabbi Yishmael & Midrash Tanchuma Buber

Another explanation. Why did Scripture concern itself with the genealogy of the chiefs? Did the Holy One, blessed be He, have nothing else to write about other than the chief of Timna, the chief of Lotan, etc.? He did so to teach us that from the very beginning of the creation of the world, the Holy One, blessed be He, concerned himself with the genealogies of the idolatrous nations so that it would not be left to them to describe for mankind their sterility and their degeneracy. How did He do that? When He came to the genealogy of the sons of Ham, He said: The sons of Ham: Cush, and Mizraim … and Cush begot Nimrod (Gen. 10:6–8); thus He indicated that they had become defiant, as it is said: He began to be a mighty one in the earth (ibid., v. 8). Similarly, when He said: And Mizraim begot Ludim … whence went forth (ibid., vv. 13–14), He did not say “he bore him” but he went forth, thereby informing us that he was the product of an incestuous relationship.

(Ib., ib., ib.) Now Hebron had been built seven years before Zo'am in Egypt. What does was built mean? Can it be taken literally? How is it possible that a man should build a house for his minor son, before he builds one for his grown-up son? For it is written (Gen. 10, 6) And the sons of Ham: Cush, Mizrayim, and Put, and Canaan. [Hence we see that Canaan was younger than Ham]. We must therefore say that she was fruitful, seven fold, over the city of Zo'an, and although there is no more stony place in the entire land of Israel than Hebron, this is the reason why it was devoted a cementery, and again there is no better land in the entire Asiatic region than that of Egypt, as it is said (Ib. 13, 10) Like the garden of the Lord, like the land of Egypt; and there is no better ground in the entire land of Egypt than that of Zo'an, as it is written (Is. 30, 4) For his princes were at Zo'an. Nevertheless Hebron was seven times as rich in fruit production as Zo'an. Is this a fact that Hebron contains stony ground? Behold it is written (II Sam. 15, 7) And it came to pass at the end of forty years, that Abshalom said unto the king, 'Let me go, I pray thee, and fulfill my vow, which I have vowed unto the Lord at Hebron; 'which was explained by R. Ivia, and according to others by Rabba b. b. Chana that this means: "He desired to go to Hebron to bring sheep for an offering." And we are also taught in a Baraitha that rams came from Moab and sheep from Hebron [hence we see that it contained pasture plains]? From the very place we can infer that it was a stony ground, and just because it was stony, therefore it was devoted to pasture ground, which fattens sheep.

Whence do I derive (the same for) the first-born of Cham and Cush? (viz. Genesis 10:6) From (Psalms 78:51) "And He struck every first-born in Egypt, the first fruit of their strength in the tents of Cham."