My knowledge of the Atlantic slave trade isn't all that great, but as I understand it by the end of the 19th century it was no longer practiced by the major world powers who'd once propagated it (the US, Britain, France, Spain etc)
The thing I don't understand is that if there was a drive amongst at least some Whites to abolish slavery, why did there continue to be such extreme racism afterwards? The question seems to especially apply to America, since my limited reading has given me the impression that a big push behind abolition was done by the religious who viewed it as sinful/abhorrent to God, and yet America, despite it's largely religious population (ie the Bible Belt) has a legacy of even institutionalised racism, such as the Jim Crow laws. Why didn't the religious aspects of abolitionism take hold in such religious areas?
How was it that people were able to recognise the humanity of other races/convince others of it enough to end slavery only for entrenched racism to prevail for decades, and in some cases even to the present day? It seems that, if people realised how wrong slavery was that they would surely do away with their racial hate and beliefs. Did the abolitionist movement not actually strike a chord with most people, but was somehow able to influence governments? Was it simply a case that a few pen-pushers managed to make slavery illegal whilst the average Joe continued to hold, and pass on, racist views?
I'm understanding your question like this: Why did the religious aspects of the abolitionist movement not appeal to the common southerner who was just as religious if not moreso than his northern counterpart?
Well the main of it is that to American, Evangelical, Christians (ie most Americans at this point), the argument For slavery is much, much stronger than that of the abolitionist. The main argument used is that of "The Curse of Ham" in the Old Testament (Genesis 9-11) after the Great Flood, Noah gets drunk on wine and passes out in his tent, one of his sons Ham, sees his nakedness and tells his brothers, Shem and Japheth. When Noah awakens he is outraged and curses Ham.
“Cursed be Canaan! The lowest of slaves will he be to his brothers.” He also said,“Praise be to the Lord, the God of Shem! May Canaan be the slave of Shem. May God extend Japheth’s territory;may Japheth live in the tents of Shem, and may Canaan be the slave of Japheth.
In this passage Canaan/Ham (The African) is cursed to be the slave of Shem (The Asiatic) and Japheth (The Caucasian). As time went on, the black race was barbarized further by the inclusion of the Tower of Babel to their racial history in which the character Nimrod (grandson of Ham) is blamed for the confusion of the tongues and Gods further separation of the races on the Earth. So by using Biblical justification, they dehumanize the African race and thus make it easier for slavers to morally condone slavery. In addition to this, Biblical scholars of the 19th century point to the Many instances in the Old Testament (beyond the Curse of Ham) to argue that the Bible itself gives support to the institution of slavery. There are several instances in Leviticus that outline slave laws but do not speak against it. One good example is
Leviticus 25:44-46
As for the male and female slaves whom you may have, it is from the nations around you that you may acquire male and female slaves. You may also acquire them from among the aliens residing with you, and form their families that are with you, who have been born in your land; and they may be your property. You may keep them as a possession for your children after you, for them to inherit as property.
In terms of the New Testament, Jesus himself says nothing but it is outlined several times throughout, never in terms of abolition but rather that slaves should obey their masters yet it also indicates that there is a little bit of leeway for Christianized slaves.
1 Timothy 6:1 Let all who are under the yoke of slavery regard their masters as worthy of all honor, so that the name of God and the teaching may not be blasphemed.
Now for Americans who want to use the Bible for Abolitionary purposes, they have to contend with nearly a hundred Old and New Testament verses that allow and condone slavery (If you want a list, I can send it to you.) So this very strong Biblical defense of slavery is basically unpenetrable without going through some serious theological loops. Slavery doesn't end due to Biblical thought and analysis, it wouldn't have happened that way without a serious overturning of mainstream American religious thought, the argument for which theological argument about slavery is actually correct is solved by the Reverends Grant and Sherman from 1861 to 1865. This forceful end of slavery does nothing to change how southerners view their black counterparts but further instills hatred and racial bigotry, to them, they were justified by their view of the bible and a sufficient Biblical retort wasn't available, so the North forced them to end their institution.
Sources: Noah's Curse: The Biblical Justification for American Slavery, Stephen Haynes
The Bible
Religion in American Life: A Short History, Jon Butler, Grant Wacker and Randall Halmer