There is an intriguing new book soon to be published by Michael Knox Beran, titled "Forge Of Empires 1861-1871: Three Revolutionary Statesmen and The World They Made" in which he proposes that Abraham Lincoln saved the world.
As much as I love Abraham Lincoln, I'm not sure I'd agree that Lincoln "saved the world." On the surface, at least, it seems jingoistic at the least to claim this of Lincoln, and therefore America. This concept of "save the world" strikes me as a neo-conservative belief which leads us into unnecessary conflicts throughout the world.
Of course, it is impossible to judge the hypothesis of the author without a thorough reading and study of his forthcoming book.