I know a little about the view of north africans being cacausians but less about the broader context than I would like and would happily take corrections and additions. I'm also going to use some pretty racist language because I'm describing some pretty racist theories.

But yes Caucasian in a lot of racial theory meant indo european rather than white. So Turks, armenians, russians, indians, persians and arabs would be Caucasian.

The classic racial theory was essentially negroids, mongoloid (east asian), ameri-indian, australioid and caucasian. This is obviously something that varied depending on politics, do we want to count these people as white or not and per person but if you look at the guys who wrote a lot of this stuff in the 19th century they often had that wider definition of Caucasian.

I simply don't know enough to know to what extent Caucasian actually meant white or as a broader definition. It's worth noting that white unity was less of a thing in Europe where a lot of this was been written then it was in the empires because of inter white racial prejudice so the irish were white but still not as advanced as the English obviously etc. You saw basically a lot of stuff like the turkish and indian subraces of Caucasians, being obviously connected but still different to the Europeans. But to an extent as long as this racial structure was built by christians you couldn't remove the middle east from the white category because that's where jesus came from.

So in terms of Africa this is the Hamitic Hypothesis. As in you had the black africans and then you had the civilised africans and they weren't native they were Hamitic invaders from the middle east.

Hamites is a term from the bible, Ham being a son of Noah. In Muslim texts you often saw 'the curse of Ham' as a way of referring to black skin, this was often used to justify racial slavery as as long as a person was black they were still cursed and so could not be a free muslim (this was part of the 17th century race wars in North Africa and the dispute as to whether black muslims could be enslaved as well as black pagans). The idea that Ham had been cursed with black skin, for watching Noah masturbate, is an old jewish myth.

This was the original idea of the black africans, they were the sons of ham, cursed by god to be slaves. Because humans had began in the garden of eden, in the caucus mountains, the black africans were old and degraded having travelled further from their origin and thus strayed further from god. You got some push back against this as not being racist enough because it claimed a common ancestry between white and black people. The blacks were still human not a separate creation. But by and large this was reasonably uncontroversial among the people who cared about racial classification through a biblical lense.

But then Napoleon invaded Egypt and more and more stories about the Pyramids and the old cities are being told in Europe and originally this was seen as a negroid civilisation but that's a dangerous thought. So if Ham's children created these great civilisations in North Africa was Ham a negro? Obviously not, so you saw instead the theory that it was only Ham's son Canaan who was cursed. The Negroids were the descendants of Canaan only, Ham's other sons would give birth to the Copts of Egypt and the berbers of Morocco and the like.

It was WG Browne who argued that actually egyptian and arabic are very similar languages and the Ethiopian languages are very similar as well. So the North Africans probably are from Arabia originally, I mean look at all their achievements they must have been.

So this was the story of African civilisation as best summed up in The theory of Conquest of Inferior by Superior Races by John Henning Speke . Obviously black africans couldn't have built any cities so it was Hamitic middle eastern invaders who created any kind of major state and the negroids were just dumb workers in those empires, all african achievements happened because they were conquered and 'uplifted' by the middle east Hamites. So obviously North Africa, home of Carthage and Rabat and Cairo would be Hamitic and so caucasian. Ethiopia, Somalia, Sudan and Mali also had ancient cities so would also be this.

Further south is when it gets ridiculous. So the abandoned city of Great Zimbabwe deep into the south of the continent, that was the remnants of a Hamitic civilisation that no longer exists. The Swahili cities in Kenya, and Tanzania, they're persian Hamitic settlers. The sophisticated great lakes aristocracy of Uganda and Rwanda, they're Hamitic but the non aristocracy aren't (this hypothesis led to the Hutu and Tusti social divide being racialised, the idea was that the Hutu were African but the Tutsi were Hamitic. Obviously this had consequences as a world view in the form of four attempted genocides.)

As Charles Seligman put it in the 1930 Races of Africa 'the only civilisations of africa are the civilisations of the hamites'.

For obvious reasons black african historians weren't entirely happy with this world view. Chieck Anta Diop of Senegal led the push against this, he wanted to claim the North Africans as Africans. Timbuktu and Addis Ababa as African cities. Reducing and narrowing the concept of being Cacausian was seen as a needed response to racist pseudo history that expanded that concept in order to remove accomplishments from other races to claim they had none.

Main sources here are Edith Saunders and Michael Spottel