You might check this would-be bibliog for an historical novel.

In the first place, starting around #14, in puts together the most-recommended books from AskHistorians' reading list. That's your balanced debates

In the second, it links in a lot of primary sources, esecially those of the abolitionists. They felt the main purpose of the war was to conquer a huge territory that could all be made slave cotton plantations. Cotton, as then raised, exhausts the land, leaving the cotton planters constantly looking for new land out west. They had already claimed Texas, which rebelled when Mexico outlawed slavery. After the war, abolitionists fought to keep the size of the territorial aquisition down, and more to the north, to thwart the slave states. Their efforts supported California coming in as one long state, free, rather than one free and one slave state.