In Lebanon there was a strong inflow of Frankish lords (and their retinues) during the Crusades. That explains why many people look European in Lebanon. Much more so than Caucasian slaves (which were more a thing in Turkey anyway, not really in Lebanon).
About Black admixtures: in general the Arab slave owners castrated their Black slaves (unlike what the Europeans did), so there were few admixtures. The Black people of Morocco (in the south of the country) never mixed with the rest of the Moroccans, and still constitute a marginalized group today.
In Algeria, the Black slaves lived on the margin of society, and when the French conquered Algeria in 1830 they were freed by the French (there's a French soldier who served in Algiers and Oran shortly after the conquest who wrote a book about what he saw, and it's very interesting how he describes the Black people in these cities, who lived on the margin on society, often doing peculiar jobs like street singers and dancers). But since most of them were castrated, the Black population of Algeria has entirely disappeared (until recently and the arrival of many Black African migrants, who are treated very badly and forced to live in shacks on the outskirts of Algerian cities).
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Racism against Black people is still extremely strong in North Africa (akin to southern USA in the 1920s). One Senegalese student in Morocco (there are more and more Senegalese students who go study in Morocco due to shared university language, i.e. French, and easier visas than going to Europe) was saying in an article in Le Monde that one day he gave some coins to an old begging women in the street (Casablanca or Rabat), and when the woman saw that, she exclaimed in Arabic "oh Allah, what a wretched woman you've made of me, now being given money by some [derogative Moroccan Arabic word for Black people]!" She didn't know the student understood street Arabic. He replied to her harshly in street Arabic, she was stunned. He said this happens frequently.
More recently, there have been social movements by Moroccans to fight against this racism, associations to protect the migrants, scandals in the media, etc. It's the North African country that is most advanced in this respect, Algeria and Tunisia are far worse, dictatorships with almost no one there helping or supporting the Black migrants.
In this video you can see some of the Moroccans helping the Black migrants (at the beginning of the video, they don't translate it, but the Moroccan trade unionist says "Us, as a trade union, we were conscious of the migrants' situation etc.").
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