Ok, so browsing reddit, I come across this AskReddit post that said "Could I destroy the entire Roman Empire during the reign of Augustus if I traveled back in time with a modern U.S. Marine infantry battalion or MEU?"
A redditor started posting a little short story about it, in day by day chunks here:http://www.reddit.com/r/AskReddit/comments/k067x/could_i_destroy_the_entire_roman_empire_during/c2giwm4
It's awesome, tell to me some books that are kinda like that. Sort of alt-history type things.
And BTW, look for that story coming to a theater near you, apparently Warner Brothers has bought the rights/screenplay from the original author to turn it into a movie.