How does Mark Twain address the question of slavery in Huckleberry Finn?

The theme of slavery is perhaps the most well known aspect of this novel. Since it's first publication, Twain's perspective on slavery and ideas surrounding racism have been hotly debated. In his personal and public life, Twain was vehemently anti-slavery. Considering this information, it is easy to see that The Adventures of Huckleberry Finn provides an allegory to explain how and why slavery is wrong. Twain uses Jim, a main character and a slave, to demonstrate the humanity of slaves. Jim expresses the complicated human emotions and struggles with the path of his life. To prevent being sold and forced to separate from his family, Jim runs away from his owner, Miss Watson, and works towards obtaining freedom so he can buy his family's freedom. All along their journey downriver, Jim cares for and protects of Huck, not as a servant, but as a friend. Thus, Twain's encourages the reader to feel sympathy and empathy for Jim and outrage at the society that has enslaved him and threatened his life. However, although Twain attacks slavery through is portrayal of Jim, he never directly addresses the issue. Huck and Jim never debate slavery, and all the other slaves in the novel are very minor characters. Only in the final section of the novel does Twain develop the central conflict concerning slavery: should Huck free Jim and then be condemned to hell? This decision is life-altering for Huck, as it forces him to reject everything "civilization" has taught him. Huck chooses to free Jim, based on his personal experiences rather than social norms, thus choosing the morality of the "natural life" over that of civilization.