To get out of slavery, it is generally safer — but not necessarily easier — to do so by legal means.
As with illegal exit, this can happen on either an individual or a mass basis. Individually, the interesting thing is that it can potentially be initiated by the owner, or by the slave. Where slaves are permitted to earn money, it’s theoretically possible for them to earn enough money to buy their own freedom. (Or that of a loved one, such as a spouse or child.) Of course, is the owner willing to sell? What price have they set on emancipation? Does the law stand ready to back a slave whose master tries to set that number unreasonably high? Does it protect the slave’s earnings, to make sure nobody interferes with their progress toward freedom? Despite the ways this can go wrong, though, it was still a valid path for many slaves in societies that permitted it.
More common, I suspect — both in the sense of being found in more societies, and more frequent even where slave-initiated freedom was possible — was manumission, i.e. the freeing of a slave by their master. Unlike the above, no financial transaction was involved; instead, in economic terms, the slave-owner just gave up a portion of their wealth. Given the monetary value a slave represented, this could be a substantial blow to the purse, especially when manumitting more than one at a time.
Lest you acquire too rosy a view of such masters, though, bear in mind that one of the most common ways to manumit slaves was via one’s last will and testament. Sure, they can go free! . . . after their owner no longer has need of them. It’s not a meaningless gesture, since otherwise the slaves would be inherited by that person’s heir and go on toiling in bondage, but it doesn’t say a lot for the moral character of the owner that they feel no particular compulsion to free everybody before their death. Alternatively, they might manumit elderly slaves, no longer of an age to work — which of course makes you wonder how those new freedmen and freedwomen were supposed to support themselves going forward.
Other masters did somewhat better. Good service might be rewarded with manumission; sometimes the trigger was a dramatic event, like saving the master from a mugger or a house-fire, or (for slave soldiers) conspicuous valor in battle, but other times it was just the accumulation of loyalty and hard work over time. Naturally, this could become the carrot dangled in front of one’s human property, promising them freedom if they’re good and obedient and don’t show too much that they resent their status. Depending on who’s doing the dangling, though, that promise might be sincere.
And there were individuals throughout history who freed their slaves for purely moral reasons. Not because they were compensated, not because the slave had earned it through service, but simply because it was the right thing to do. Though they often made up only a small percentage of their societies, they did exist; it isn’t modern sensibilities intruding on historical reality when you see a character in fiction go that route.
As you might expect, that last approach to manumission slides neatly over to the abolition side of the story. After all, if you believe it’s wrong for you to own human beings as property, you probably believe it’s wrong in general. But how do you bring about the end of slavery as a whole?
Slowly, painfully, and with great effort.
In some cases it’s driven by religious sentiment; the Quakers, for example, played a key role in ending slavery in the United Kingdom and United States. But religious sentiment can be a malleable thing, as evidenced by arguments within white Christianity over whether the Bible supports slavery (proponents cited verses where scripture approves of individuals owning slaves) or opposes it (proponents cited the overall thematic message of scripture, toward liberation and forgiveness). How was this debate finally resolved? In the words of historian Mark Noll, it was “left to those consummate theologians, the Reverend Doctors Ulysses S. Grant and William Tecumseh Sherman, to decide what in fact the Bible actually meant.”
Grant and Sherman were, of course, generals rather than religious leaders. As that quote indicates, politics and economics play an even more significant role than religion . . . but again, both for and against abolition. William Wilberforce and his coalition in the U.K. fought for twenty years to bring about an end to the slave trade — abolition of slavery itself took another twenty-six years to achieve — and when they finally achieved it, they did so in part because of the war with France. Although the French Revolution had abolished slavery, Napoleon brought it back, which gave Britain incentive to show its superior moral fiber. But the counter-arguments were that if Britain stopped trading in slaves, other countries would just pick up the slack (and with it, the profit). Meanwhile, over in the U.S. the Southern economy in particular was heavily dependent on slave labor; it took the Civil War to finally garner enough political will to make abolition a reality.
If those examples seem tilted toward the last couple of centuries, that’s because the nineteenth century saw a wave of abolitionism sweep the globe. Slavery faded in and out locally in different places at different times, but often not in ways that truly meant an end to the institution. It might still be maintained for certain groups of people, or displaced to colonies while abolished at home, or replaced by a very similar institution like serfdom (about which more in a couple of weeks), or — as with the French example — it might go away for a little while, only to come back later.
On the whole, I think the move toward abolition has to be linked to a deeper shift in human society, which has to do with something historian and SF author Ada Palmer calls the “empathy sphere.” Our sphere of empathy has been expanding for a long time, increasingly recognizing the humanity and dignity of people who are not members of our family, tribe, nation. Improved political rights for women, recognition of alternative genders and sexualities, and the push for true equality for people of color and those with disabilities are all expressions of this expansion; so, for that matter, are movements like animal rights and science fictional explorations of the personhood of AI or clones. Behaviors that used to be utterly normal and unobjectionable — like abusing animals, beating women, and exposing malformed babies — are considered far less acceptable now.
Abolition is not, in the end, ultimately about religion or politics or money. Those are factors that can help or hinder it, but slavery, at its heart, requires the masters to deny the full humanity and dignity of whomever they’re enslaving. A society that practices such denial will always find ways to slide back toward the exploitation of unfree labor, because there’s so much profit to be had. A society that shifts toward recognition of that humanity and dignity will find such exploitation untenable.
But the road there isn’t an easy one.