Currently, there are an estimated 1,500 Christian and Yazidi girls and women still in captivity, while 1,000 others are missing in Iraq and Syria. Others are believed to have been sold to sex traffickers in Turkey. It is an issue that the international community cannot ignore.

Habib, traded four times during her captivity, witnessed many cases of Christian and Yazidi girls -- some as young as 9 years old -- sold, raped and tortured by ISIS members.

Despite losing control of Raqqa and other major strongholds in Syria and Iraq, ISIS continues to keep many of the women it kidnapped during its rise in 2014. The world seems to have forgotten about them.

After more than three years, Rita Habib, a 30-year-old Christian woman from the Iraqi city of Mosul, was recently reunited with her blind father in Erbil, the capital of Iraq's Kurdistan Region. She and her father are the sole survivors of a family whose members, like thousands of Christians and other non-Muslims, was murdered by ISIS in mid-2014. Habib was among hundreds of Christian and Yazidi women and girls abducted at the time and sold into the sex trade. She was one of the lucky ones to be rescued by the Christian advocacy group, the Shlomo Organization for Documentation, which paid ISIS $30,000 for her release.

Abu Shujaa, a Yazidi activist who has been involved in rescuing hundreds of Yazidi women from ISIS, helps secure their release in various ways, but said that all require money, which is hard to come by.

When Raqqa, the former de facto capital of ISIS, was liberated by U.S.-backed and Kurdish-led Syrian Democratic Forces, many captured women were freed. Despite losing control of Raqqa and other major strongholds in Syria and Iraq, however, ISIS continues to enslave many of the women and girls it kidnapped during its rise in 2014. The world seems to have forgotten about them.

When ISIS carried out its onslaught on Yazidi towns across northern Iraq in the summer of 2014, its mission was to eliminate the kufar ("infidel unbelievers"). To this end, it forced Yazidi men and women to convert to Islam. Males who refused were murdered, and females taken as sex slaves. Christians, viewed by ISIS as "People of the Book," purportedly fared better. They were ostensibly given the option of paying jizya, a form of Islamic protection tax, as an alternative to death, for the "privilege" of living under the rule of ISIS's so-called caliphate. Such claims, however, were apparently just propaganda: all Christians were forced to convert to Islam; Christian girls and women, as with Yazidis, were forced into sex slavery.

Habib, traded four times during her captivity, witnessed many cases of Christian and Yazidi girls -- some as young as 9 years old -- sold, raped and tortured by ISIS members.

At one point during the peak of the conflict, there were nearly 7,000 non-Muslim females captured by ISIS. Currently, there are an estimated 1,500 Christian and Yazidi girls and women still in captivity in Iraq and Syria, while 1,000 others are missing. After their defeat in Raqqa, ISIS jihadists reportedly moved most of the captive females to other areas under their control in eastern Homs and southern Damascus. Others are believed to have been sold to sex traffickers in Turkey.

With the anti-ISIS campaign gradually dwindling, many Christian and Yazidi groups fear that discovering the fate of those girls and women still in ISIS captivity is becoming even more difficult. It is an issue that the international community cannot ignore.