You see neither alternate cartographer went into much detail about why there was a "Second American Civil War" in the first place. Looking at the first map and second map together, you get the idea there was a lot of changes in the 1930s. An America without a New Deal, an Imperial Japan that avoided war in China and a Soviet Union that defeated Nazi Germany and "liberated" Europe on its own are just a few possibilities. I can't pin point an exact POD that would lead to MacArthur taking over America in 1940, but certainly there were a lot of changes that would make a great alternate history if anyone decided to flush out the timeline.
Honorable mentions this week go out to Bruce Munro's map (description here) on a more plausible Crystal Empire by L. Neil Smith. If you want to submit a map for the next Map Monday, email me at ahwupdate at gmail dot com with your map attached and a brief description in the body of the email.
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Matt Mitrovich is the founder and editor of Alternate History Weekly Update and a blogger on Amazing Stories. Check out his short fiction. When not writing he works as an attorney, enjoys life with his beautiful wife Alana and prepares for the inevitable zombie apocalypse. You can follow him on Facebook or Twitter.