The Guns of the South by Harry Turtledove

http://en.wikipedia.org/wiki/The_Guns_of_the_South#Awards

This book rocks, and it seems somewhat relevant to a lot of the stuff we're talking about (in an historical fiction kind of way). It takes place during the Civil War, and these people show up and start giving AK-47's to the South in an attempt to make sure they win. As it progresses, it is revealed that these mysterious people are actually time travelers from 21st century South Africa, and they've come back to rewrite history in favor of whites over blacks. These time travelers buy plantations and slaves and some of the whites in the South begin to question things because they see how poorly they're treating their slaves (aka torture.) Spoiler alert! The story ends up with the South abolishing slavery despite all of these time travelers and their technology and intelligence supporting slavery, and so the story ends on a surprisingly happy note.