I have heard all of my life that the Civil War was necessary to free the slaves in the United States. Not whether the war was about freeing the slaves, but the necessity of that action to cause their freedom. Greatest Emancipations is a description of the freeing of slaves in the US, by Great Britain, in Haiti, Cuba and the Belgian Congo. The book goes into some detail about the ruthlessness of the practices of the slave traders and owners, which is a reminder, lest anyone forget, just how inhumane this practice was.
The largest credit for the ending of the slave trade unavoidably belongs to the leadership of the abolitionists in Great Britain. They worked the longest and at great personal risk to rid the world of the horrific trade in slaves.
A combination of international pressure and slave rebellions seemed to work in different places in different proportion to bring about the ending of the practice. While Haiti was torn by Civil War, it was led by factions of slaves as well as slave owners, rather than by a central government as in the US.
What surprised me most was how Belgium got into the slave trade in the Congo so late and so brutally, beginning and ending at the evil desire of King Leopold.