The nature of pre-Civil War life is shown very strongly through this text thanks to the geography of the escape that Huck and Jim try to embark upon. Initially they decide to escape to Cairo, Illinois, as this is a city in one of the Free States where Jim could be free and would be able to not have to worry about being hunted down by slave traders. However, unfortunately, they miss Cairo in the fog that descends upon them in Chapter 16:
When it was daylight, here was the clear Ohio water inshore, sure enough, and outside was the old regular Muddy! So it was all up with Cairo.
Although the text records Jim's unhappiness with missing the city of Cairo in the fog, it is absolutely vital to realise that this was the one chance of freedom he had. Unfortunately, with the disappearance of the canoe and then steamer crashing into their raft, Jim and Huck never get a chance to head back up North towards Cairo, which represents the best chance of freedom and therefore reunification with Jim's family that he has. Therefore, in understanding this novel as a picture of pre-Civil War life, it is important to see it as a depiction of an America divided into Free States and Slave States, where standing on one side of a border could dramatically alter an African-American's life.