How does To Kill a Mockingbird deepen one's understanding of the past?

The book works on many different levels, one of which is historical. To Kill a Mockingbird gives contemporary readers a unique insight into life as it was lived in countless small towns across the Deep South in the 1930s. This was a very different time to ours, a time in which racial segregation was deeply entrenched and racist, prejudiced attitudes were the norm.
But To Kill a Mockingbird isn't a work of history; it's a novel. And as it's a novel it uses the experiences of its characters, most notably Scout, to give us a better understanding of a dim and distant past. As the book opens, most readers don't know what it's like to live in a town like Maycomb. (At least one hopes not). But thanks to Harper Lee's rich characterization and unerring eye for detail, we gradually become more and more aware of the strange rhythms of this world, how people interact with each other, the values they hold, and so forth.
Though Maycomb is not a place where many of us would want to live, by the time we reach the end of To Kill a Mockingbird we can at least understand its history much better than we did when we started reading the story. If we've been paying attention, we will have taken to heart Atticus's valuable lesson in putting yourself in other people's shoes. It is this empathetic approach which is often used in history lessons as a way of understanding the past, and is used by Harper Lee to good effect in telling the story of the world in which she grew up.