Muslims, whites, blacks: all guilty!
Bear in mind, however, that we cannot judge history in the light of current values or through today's rosy lens!
The slave trade has always been a common practice within African societies, from long before the arrival of Arabs and Westerners, until long after they left... This practice, which is currently illegal, continues today, unfortunately. It is estimated that, thanks mainly to the action of Africans and Muslims, humanity has never had as many slaves as it does today.
The African tradition has always been to turn people into merchandise.
Millions of Africans were subjected to slavery by other Africans: way more than 20 million. Slaves were usually captured during the endless wars between African nations and tribes. But many of the tribesmen themselves were made slaves by their own tribal chiefs, for economic purposes.
The arrival of Muslims in Africa, in the 7th century, simply increased the capture of slaves, and the respective trafficking started to be dominated by the Arabs, until the arrival of Westerners in the 15th century. Despite having lost control of the slave trade at that time, the truth is that Muslims continued to enslave millions of blacks until the 20th century.
Between the 7th and 16th centuries many whites were themselves enslaved, mainly at the hands of Muslims but even by Africans themselves. During that period, the number of Westerners enslaved by Muslims is estimated at over 2 million.
With their arrival, in the 15th century, the Westerners took control over the slave trade, thus wallowing in barbarism. Westerners, however, did not go into forests or savannas to capture black people. They simply bought the slaves from the blacks themselves!
The creation of human rights and the abolition of slavery are both the responsibility of Westerners. Thanks to the exclusive intervention of whites (Westerners), and for the first time in human history, slavery was abolished and several fundamental human rights were instituted.