To show the shortcomings of the 19th century in American life, Mark Twain uses "Satire" in his novel "Adventures of Huckleberry Finn", as a literary device to criticize American society at that time.
The "Satire" exerts humor, irony and ridicule to reveal and point out flaws in political contexts and other particular issues.
Although there are some traces of "Allegory" as well; a story revealing hidden meanings, generally morally and politically angled.