There is many verse with the Quran seeking freedom for slaves: 90:13 58:4 9:60

Marriage in Islam is slavery.

Give them time, Islam is a newer religion. it's 500 years newer than christianity and yet christian nations only started freeing slaves as recently as 200 years ago.

Because it's an ancient religion. Although muslims are not allowed to enslave other muslims.

1) For the same reason that it is not prohibited in Christianity. Notice that it was not the Church which decided to abolish slavery. Like Christianity, Islam appeared in a world where slavery was broadly widespread, and they just did not suppress it. 2) "The historian Bernard Lewis notes that both the Old and the New Testaments recognize and accept the institution of slavery as allowable under certain circumstance (Leviticus 25:44-46; Exodus 21:7-11). Yet, the Bible was used, before and during the American Civil War, by both slaveholders and abolitionists to justify their views." "For centuries, the narrative of the “curse of Ham” has been continuously cited as the justification for black slavery. The story has repeatedly been interpreted as God’s condemnation of the black race as a result of their progenitor’s crime against family and honor. The basis for Ham as the origin of the black race depends on the assumption that many of the ancient Israelite authors made, primarily that all of humanity descended from Noah’s three sons (Shem, Ham, and Japheth) who were among the chosen few to have survived the Great Flood. The passage (Genesis 9: 18-27) corresponds to the Jahwist’s narrative technique of cause and effect/ crime and punishment form" 3) "In certain circumstances, Islam allows for slavery. Such slaves may in some cases be able to purchase or acquire their freedom in various ways. The prophet Muhammad owned several slaves himself. One of them bore him a son, who died as an infant. The slavery endorsed by the Qur'an limited the source of slaves to the children of two slave parents and non-Muslims captured in war. The Qur'an provides for emancipation of a slave as a means (or in one case, a requirement of) demonstrating remorse for the commission of certain sins. Proclamations of emancipation and repudiations of participation in slave trafficking did not occur in Muslim lands until after the Christian-European Colonial era - as late as 1962 in Saudi Arabia, 1970 in Oman and Yemen, and 1981 in Mauritania. Islamic slavery in the fashion multigenerational hereditary slavery (in Mauritania) is still evident today. In Chad, child enslavement with the aspect of forced conversion to Islam has been documented." Source and further information (2 & 3): http://en.wikipedia.org/wiki/Slavery_and_religion

Hmm! Who would do the cheap labor?