It is necessary to end this eternal propaganda by Muslims that it was "only" Islam which first ended the discrimination against the blacks, and thus it is a proof that Islam is a divine religion.

It is absolutely not correct, while even before Islam, in ancient Arab Culture the discrimination was on the bases of being Free or Slave, otherwise Black people could be Free, and could be kings and could marry the Arab women.  White slaves had no worth as compared to the Black Masters.

In comparison to the Free/Slave thing, the discrimination on the bases of colour was NEGLIGIBLE.

The ancient Arab tribal culture was inferior to the culture of the other areas in that region. For example, Abyssinia, which had a black person (Najashi) as a King and which was a proper STATE as compared to the tribal culture of Arabs. And Muslims themselves came to Najashi (the black King of Abyssinia) to seek refuge, and they were indebted to him for protecting their life. And you could not put the status of a person lower to your own status to whom you are indebted. 

Bilal (the black companion of Muhammad) also belonged to Abyssinia. But perhaps the biggest factor was this that Umm Ayman (the foster mother of Muhammad) was also a black from Abyssinia. Muhammad played with his black foster brothers and sisters as child. 

And not only ancient Arabs, but also the Judaism and Christianity also didn’t discriminate on the basis of colour and gave rights to the black people to be free, or to even become king and marry white people. In bible there are many black characters like Queen of Seba, Zipporah, Ham etc. And Hajar, the mother of Ishmael (whom Muslim consider to be forefather of Arabs) was herself a black woman.

Muhammad claimed that Islam follows the same God of Judaism and Christianity. Since there was no open racism in those religions against the black people too, and the King Al-Najashi of Abyssinia was himself a Christian, thus again it made difficult for Muhammad to introduce any open racism against the blacks in Islam.

That is why Muhammad was unable to stop the black people to stay Free, or to become king, or to marry the Arab women, or to buy Arab women as slave, but still Muhammad followed the Arab culture and continued with the ignorant beliefs of taking Black sheep for sacrifice (Sahih Muslim) and declared Black Dogs to be evil Satans (Sahih Muslim).

Therefore, there was no heroic deed by Muhammad, but he was only following the old Arab customs. As far as discrimination is concerned, then Islam showed so much DISCRIMINATION in name of slavery that it became a real shame for humanity, where Islam took away the right from slave women to dress properly, where Islam made them naked and placed them topless in the markets of slavery, made their rape Halal by all masters, and even took away their small breastfeeding children and sold them in the slave markets.

SEVERUS: ROME’S FIRST AFRICAN EMPERORPlease also note, that even the Roman Empire had the black Emperor SEVERUS before Muhammad. And there were African blacks in Roman Empire, who were soldiers, and citizens, and some had also the prestigious posts (link). 

And not to forget the 5 black Pharaohs of Egypt. They were (link):

  • Pharaoh Kashta 760 – 747 BC. Kashta, the brother on of Alara, who ruled Egypt in a time of turmoil and destruction. …
  • Shabaka 712 – 698 BC. …
  • Tarharqa 690 – 644 BCE. …
  • Tantamani 664 – 657 BCE (Last Pharaoh of the 25th Dynasty)

Superiority of the race of Arabs over non-Arabs

But Islam does have a special Racism in it, which is known as "Arab Racism".

Please read about it here:

1) The Arabs Are Superior In Islam

2) Superiority of the race of Arabs over non-Arabs

Islam Apologists: There was still significant Racism present against Black People

Islam apologists disagree and claim that still there was significant racism present against the black people in Arab society and Islam ended it.

As proof, they present the following tradition and claim that this tradition clearly shows that at the time Black slaves were considered less than Arab slaves.

Sahih Muslim, Hadith 1602:
Jabir (Allah be pleased with him) reported: There came a slave and pledged allegiance to Allah's Apostle (ﷺ) on migration; he (the Holy Prophet) did not know that he was a slave. Then there came his master and demanded him back, whereupon Allah's Apostle (ﷺ) said: Sell him to me. And he bought him for two black slaves, and he did not afterwards take allegiance from anyone until he had asked him whether he was a slave (or a free man)

Problem is this that this hadith is not saying that two black slaves had a worth of one Arab slave as the interpretation of Islam apologists is. We don't even know that the first slave was even an Arab in the above tradition. And this case may be an "exception" where the price of that first slave increased due to his acceptance of Islam.

Thus, it may be an exception, which was similar to when Muhammad gave 7 slave women to companion Dhiya in order to get one beautiful Saffiyah (Sahih Muslim)

The 2nd (and last) proof by Islam apologists is the following tradition: 

Sahih Bukhari, Hadith 696:
Narrated Anas bin Malik: The Prophet (ﷺ) said to Abu-Dhar, "Listen and obey (your chief) even if he is an Ethiopian with a head like a raisin."

What is wrong with this one? This actually is saying obey your leader no matter his appearance and race. Black people were leaders and kings at that time, and off course obedience was demanded irrespective of their appearances. 

Conclusion:

Bottom line is this that the major discrimination present at that time in Arab society was "Free vs Slave". In comparison to the Free/Slave thing, the discrimination on the bases of colour was NEGLIGIBLE

And Islam is full of discrimination against the slaves, which indeed proves that Islam is not a divine religion, but a manmade religion.