One of the great aspects of this novel is that it is set in a real historical context, and this historical context exerts considerable influence on the characters. One of the biggest examples is of course Jim's bid for freedom and how he tries to head north towards the states where slavery now no longer exists to prevent being captured and taken back to Miss Watson for a reward.
Note for example how they talk about reaching Cairo in Chapter 16. This was a city on the edge of the free state of Illinois, and represented Jim's best chance of finally achieving freedom and being able to start a new life:
I got to feeling so mean and miserable I most wished I was dead. I fidgeted up and down the raft, abusing myself to myself, and Jim was fidgeting up and down past me. We neither of us could keep still. Every time he danced around and says, "Dah's Cairo!" it went through me like a shot, and I thought if it was Cairo I reckoned I would die of miserableness.
Huck is of course experiencing mixed emotions as he does not know whether it is a good thing for Jim to reach safety or not, because to him, from his perspective, Jim is Miss Watson's property.
An excellent way you could turn this theme of slavery and freedom into a paper would be to explore the journey that Jim and Huck make on their raft, relating it to which states were free at the time and the way that attitudes to slavery legally changed during this period, relating it to the geography of the States. Good luck!