I have friends who seem to always latch onto the popular historical revisionist theory of the day. I'm looking for some good clearly laid out analysis of such things. For example, the [analysis this subreddit provided of Menzies 1421 book] (http://www.reddit.com/r/AskHistorians/wiki/theory#wiki_historians.27_views_of_gavin_menzies.27_.221421.3A_the_year_china_discovered_the_world.22) from the FAQ is an excellent example of what I'm looking for. It doesn't matter if the analysis supports or debunks the revisionist claim, I just want some good examples of how to go about thinking critically about such claims to try and educate my friends.