If the former, for America, I agree with the Hawthorne and Twain works mentioned. I would add:
* Last of the Mohicans by James Fenimore Cooper and his other novels of the 18th century frontier. I know a lot of people can't stand reading Cooper, and Twain famously eviscerated everything he wrote. But if you take it for what it is, knowing the tastes and style of the time, Last of the Mohicans can be an enjoyable adventure story. The plot is actually relatively fast-paced, although it's hard to read quickly because of his verbose, sometimes convoluted sentences. You can definitely trace his influence down to the Westerns of the 20th century and even the modern thriller and adventure genres.
* Gone With the Wind is an obvious one, although I'm ashamed to say I haven't gotten around to reading it yet.

* Esther Forbes's Johnny Tremain is a children's classic of historical fiction. She does a great job of capturing the themes and aura of the revolutionary period in Boston, neither excessively lionizing the patriots nor demonizing the redcoats, and also shows realistic character growth and development as Johnny matures and experiences the horrors of war.
Depending on how much time has to have passed between the events in the story and its publication, there are two that might also qualify:
* To Kill a Mockingbird by Harper Lee, set in the 1930s but published, I believe, in the early '60s. Probably my favorite novel of all time, along with millions of other people!
* Red Badge of Courage by Stephen Crane, published about 30 years after the Civil War. I recently re-read this to get a feel for a young man's state of mind going into his first battle and found it vivid and compelling.