What is the main theme of The Adventures of Huckleberry Finn?

As with most works of literature, Adventures of Huckleberry Finn incorporates several themes developed around a central plot to create a story. In this case, the story is of a young boy, Huck, and an escaped slave, Jim, and their moral, ethical, and human development during a journey down the Mississippi River that brings them into many conflicts with the society around them.
What Huck and Jim seek is freedom, and this freedom is sharply contrasted with the existing civilization along the great river. This conflict between freedom and orderly civilization forms the overarching theme of the novel.