ISIL was depending on Moslem scripture to justify this. Actually, ISIL is not alone as there is still a lot of slavery in the Islamic world. There is also a lot of hatred for non-Moslems especially those they consider pagans. ISIL considers the Yazidis pagans. It was with Yazidis that ISIL reintroduced slavery (of non-Moslems, especially “pagans” like Yazidis) into their new Islamic State. This may appall many in the West and to placate foreigners most Arab nations have outlawed slavery, despite the fact that it still exists and continues to exist with much local support.
For example Mauritania held elections in 2006 and became the only other, besides Iraq, freely elected Arab government. Despite that, slavery still exists there. The divisions in Mauritania, with a population of less than four million, are between the Arab (about a third) and “former slaves” (black Africans from the south).
Mauritania exists on the border between Arabs and Bantu (the ethnic group that predominates in Africa south of the Sahara). Blacks were the slaves, and slavery was formerly abolished only in 1981. But slavery still exists in Mauritania.
In Sudan the pro-Arab government has used slavery to encourage Arab tribes to make war on darker skinned “African” tribes. The government allowed any captives taken to be enslaved. This was unofficial as Sudan has technically outlawed slavery.
It’s not just Mauritania and Sudan that have problems with slavery. In 2010 Yemeni anti-slavery groups forced their government to investigate families living in the countryside that were still keeping slaves. At least 500 Africans are believed to be enslaved, some of them recent migrants, others the descendants of slaves.
Slavery was outlawed in Arabia in the early 1960s, but that only eliminated the more obvious cases in urban areas. The practice continued in more remote areas. It’s been going on for thousands of years, during which Arabs are believed to have enslaved up to 20 million Africans. As a result, up to twenty percent of the people in Arabia appear to have African ancestors and genetic studies have confirmed this.
Culled from: http://www.strategypage.com/htmw/htmurph/articles/20150714.aspx