How does Thoreau express his ideas about slavery in Walden?
Because of his Transcendentalist philosophies, Henry David Thoreau was anti-slavery, believing that man was intended to find his own destiny and his own spiritual meaning separated from the pressures of society. This meant that Thoreau found slavery inherently immoral, less from its sociological perspectives or general cruelty than for its idea that any man could be owned by another, thus limiting the spiritual growth and personal achievement of the owned man. In Walden, Thoreau writes:
...worst of all [slavery] when you are the slave-driver of yourself! ... Look at the teamster on the highway... his highest duty to fodder and water his horses! ... See how he cowers and sneaks, how vaguely all the day he fears, not being immortal nor divine, but the slave and prisoner of his own opinion of himself...
(Thoreau, Walden, Google Books)
Here, Thoreau equates African slavery to the moral slavery of commerce, "masters" (including simple employment), and of fearing man and public opinion rather than fearing the lack of personal growth he saw in many otherwise-normal men. In his view, the slavery of all men under public opinion was as bad as actual slavery, since it is unconsciously accepted as part of the normal course of things. African slavery was overtly cruel and evil, and could eventually be recognized as such, while the slavery of commerce is ignored and even praised. This view is in line with his general philosophies of individual responsibility, freedom, and divine purpose.
Thoreau was vehemently anti-slavery, yet when he speaks of it in Walden he can sound almost flippant. Nothing, however, could be further from the truth. Thoreau is making a profound point: that until individuals who are legally free learn to respect themselves and their own dignity, slavery will remain acceptable. Thoreau writes,
I sometimes wonder that we can be so frivolous, I may almost say, as to attend to the gross but somewhat foreign form of servitude called Negro Slavery, there are so many keen and subtle masters that enslave both north and south.
Thoreau speaks of the cruelty of the southern overseer of the slaves but also of the northern master and of the way individuals enslave themselves. He notes the large number of so-called free men who are in debt to mortgages or have taken out other loans that force them to overwork themselves, saying it is commented on as unusual when a man actually owns his own farm.
This ties slavery to a central theme of Walden: simplicity. "Simplify, simplify," Thoreau commands. If people would realize how freeing it is to want less, they would learn to see life clearly and thus would come to own their own souls. This would ripple out into society. Thoreau suggests that people who live simply would no longer enslave either themselves or other people in the quest to have things they don't really want or need.
Thoreau speaks explicitly, though briefly, to the enslavement of African Americans in Walden's longest chapter, "Economy." Thoreau was an abolitionist, but Walden is a work more concerned with a philosophy of living for all of humanity. Thoreau's focus in Walden was that "what a man thinks of himself, that it is which determines, or rather indicates, his fate."
Thoreau acknowledges in Walden that "it is hard to have a Southern overseer; it is worse to have a Northern one; but worst of all when you are the slave-driver of yourself." Implicit in this statement is the idea that all men, including slaves, must re-conceptualize themselves as independent and free beings in their minds, no matter their physical circumstances. Thoreau believed that men must not only have beliefs, they must act on their beliefs. This idea was more explicitly stated in Thoreau's 1854 speech "Slavery in Massachusetts" when he said, "The law will never make men free; it is men who have got to make the law free." Thoreau comes out against any institutionalized oppression that suppresses mankind's natural divinity, whether it is public opinion, dependence on others, or our own willingness to surrender our personal liberty for material gain or security.