The Laws and rules laid out in the Quran and hadith concerning captives, those enslaved in war was always said by Muslims that at the end Islam as a religion provided to gradually eliminate slavery.
Many non-Muslim scholars from the past century, who have studied the Quran and Hadith literature carefully have come to conclude that Islam came to abolish slavery. Professor Bernard K. Freamon states,
“These verse do not emphasize notions of ownership or the proprietary aspect of the slave’s relationship with his or her own but rather highlight the debasement, degradation and stigma associated with enslavement, urging the believers to lift slaves from these conditions. Several of these verses mandate the freeing of slaves as expiation for sin or crimes and they also establish the emancipation of a slave as a meritorious and pious act, entitling the emancipator to favourable treatment in the life. For example, in verse 4:92, the lawgiver uses the important verbal phrase ‘tahrir’ (‘liberation’) to describe the action toward slaves required of one who commits an unintentional homicide. In these verses we see the underpinning for jurisprudential argument that the QURANIC VISION OF THE VIRTUOUS SOCIETY IS THAT OF A SOCIETY THAT IS SLAVE-FREE. The Linguistic typology I have outlined shows that the Qur’an acknowledged the ownership interests of the slave-holders in their human property, while simultaneously showing a great solicitude for the welfare of the slaves and encouraging an emancipatory ethic in the behaviour of their owners. Although the law in the pre-Islamic slave systems also counselled kind treatment of slaves, recognition of their humanity, and, in some cases, emancipation, these systems did not incorporate the idea of emancipation into standards of piety and human behaviour with the KIND OF VIGOR SEEN IN THE QUR’AN.”
Scholar Bernard K. Freamon, attaches in his footnote section 55, many non-Muslims who also came to the same conclusion that Islam came to end slavery:
“55 Many scholars, Muslim and non-Muslim alike, have made this argument in recent times. The argument is presented well, using Hadith sources, in the Quranic commentary of Sayyid Qutb, the late Egyptian theologian and Quranic scholar. See Sayyid Qutb, In the Shade of the Qur’an (M. Adil Salahi & Ashur Shamis (trans.), Idara Ishaat E Diniyat (P) Ltd 1992) 176-179. The British abolitionist C. W. W. Greenidge, in his magnificent little book on slavery, C. W. W. Greenidge, Slavery (Macmillan 1958), also cites several rather convincing assertions of this argument. In addition to relying on the assertions of Syed Ameer Ali, the Indian Islamic modernist, he quotes Eldon Rutter in saying ‘the Koran rightly practiced would soon bring about the complete cessation of slavery.’ Ibid 65 (quoting Eldon Rutter, The Holy Cities of Arabia). He also quotes Bertram Thomas, ‘another sympathetic authority of Arabia’, who said: ‘In the abatement of slavery Arabia has been false to her Prophet’. Ibid (quoting Bertram Thomas, The Arabs). See also Muhammad Rashid Ridda, The Muhammadan Revelation (Al Saadawi Publications 1996). Rida, another well-known early twentieth-century Islamic modernist, asserted that the Qur’an has ten purposes and one of those purposes is the elimination of slavery.” 
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 The Legal Understanding of Slavery: From the Historical to the Contemporary [Oxford, 2012] by Professor Bernard K. Freamon, page 51 – 52
(1) – LINK – “Debunking a Myth: The Irish Were Not Slaves, Too”(NYT) 17th March 2017
(2) – LINK – “WORD OF FAITH CHARISMATIC CHURCH IN NORTH CAROLINA CAUGHT RUNNING A BRAZILIAN SLAVE TRADE RING” (* *)24th July 2017
(3) – “Slave owner compensation was still being paid off by British taxpayers in 2015” (14th February 2018) https://www.rt.com/uk/418814-slave-compensation-bristol-taxpayer/