Historically how was the continent of Africa seen? Did other civilisations recognise “Africans” as an independent polity? Was North Africa seen as its own distinct subcontinent? Was Africa associated with “Blackness”?
While there will always be more that needs to be said on this subject, I recommend starting off with these posts:
On the (un)helpfulness of the standard isolation of North Africa from Sub-Saharan Africa in historiography by /u/commustar
To what extent were the Romans in contact with native African tribes? How deeply did Rome explore, but not necessarily conquer or colonize, the African continent?, on Sub-Saharan Africans in the Roman Mediterranean and on race and skintone in Greco-Roman Egypt by yours truly
Please bear in mind this is a very simplified answer and there are many points that would really benefit from a more detailed explanation. This is by no means an exaustive answer, since your questions, while compelling, are also really ample in scope!
That said, let's get to them, first things first: The notion of Africa as we know it today, as acontinent, or rather as an unifying entity that encompasses the whole of the societies, their cultures and histories that existed in that area, is a product of colonialism. As an european construct formulated for administrative and political purposes, the concept of Africa is elaborated after imperialistic domination led to the blurrying of borders, the erasure of traditions and cultural elements and the forced mingling of ethnical groups despite possible previous mutual indispositions.
These processes led to the first generation of post-colonial african historians and politicians to try and formulate historical narratives that denied eurocentrism by affirming african agency and celebrating their achievements. This historiographical effort, led mostly by Joseph Ki-Zerbo and his group, intended to retake the concept of Africa and make it into a cornerstone for the building of national and pan-african identities. More recent historiography points this ressignification process as a consolidation of the notion of Africa as we know it today, a homogeneizing representation to many different ethinicities, cultures, societies and historical trajectories.
This is all to say that until very recently, the continent of Africa wasn't particularly seen as one thing or another because it wasn't conceived as such. Up until the nineteenth century, there was no idea of the continent of Africa as a single entity among europeans. What there was is the understanding that in those lands existed tribal groups, kingdoms, empires, caliphates, etc, and these weren't necessarily understood to be related to one another, in much the same way that different european kingdoms weren't seen as part of a greater body, despite sharing sociocultural similarities among them.
The great posts linked by u/cleopatra_philopater deal with how multiple perceptions about the different african ethinicities and societies went in Antiquity, and also with the matter of how african geography stablished natural regional divisions and populational and economical fluxes on the continent. I'll focus on what I know best, late medieval and early modern periods.
North African societies being more well known in Europe for their mediterranean presence since Antiquity, a more interesting question is how aware late medieval europeans were of sub-saharan african people. A possible answer is that the former knew the later existed to some extent, even if in a very limited or mythical way. For example, some sources mention the Kingdom of Ethiopia - be it tied to the legend of Prester John, which circulated both orally and in writing at least since the twelfth century; or in hagiographical narratives present in Jacobus da Varagine's Legenda Aurea that represented it as a land where there were demons, for instance.
Contact and awareness grew considerably during the early modern period, seeing as the Portuguese, Spanish and later English empires set up trading posts and forts all along the western african coast to viabilize and safeguard the slave trade.
This ties in with your question about the recognition of african polities as independent - taking into account the narratives about powerful african kings that circulated since the Middle Ages; the fact that actual european presence in african lands was considerably limited until the nineteenth century colonization process allowed them to exert actual domination on the continent; and that up to that point in time European agents such as soldiers, administrators and merchants had to mostly work within the limits imposed by the rules of the lands where they acted, the answer to the question is yes, in most cases they did recognize the sovereignity and independence of the polities they dealt with. One could argue Europeans did so because they were forced to by circumstance and/or convenience, but the fact of the matter is they knew they were dealing with governing bodies capable of producing and enforcing their own laws and customs, and respected these while on their lands. This would change with colonial domination, but then the process of replacement of previous political structures and erasure of ethnical identities would begin to give rise to the imperial concept of Africa.
Bibliography:
["A Pirâmide Invertida"](http://docs12.minhateca.com.br/790603566,BR,0,0,LOPES,-Carlos.-A-piramide-invertida...(p.-21-29), by Carlos Lopes. A paper in Portuguese about early post-colonial african historiography and the transition to more recent productions. Sadly, it's probably unavailable in English.
"Legenda Aurea", by Jacobus da Varagine.
UNESCO's General History of Africa Collection, vols. I, IV, VI, VII.