Jay Winik gives greater focus to those events with context and proposes that we easily could have been a country in a continuing, decades-long guerrilla war that may still have resulted in two or more federated governments within what is currently the continental United States.
This is not dry history. He goes back to the country's founding and makes a pretty good case that the founders were unsure a federation of the scope of 13 individual states could remain as one for any length of time. Almost immediately, states made noises and some efforts to break away, and these were all in the north east! When we finally split in 1861, you had the 4 years of bloody fighting east of the Mississippi River but also had a terrible guerilla conflict west of the Mississippi for most of that same time. If you've seen the movie "Lincoln" you know the passage of the 13th Amendment was a very iffy thing. Had it not passed when it did, there's no telling what would have happened once he was killed, even including the following amendments that gave greater rights of citizenship to freed slaves. Finally, General Lee was ordered to take his army and melt into the mountains and fight a guerilla war, as were the other generals leading major armies in the field. Lee ignored that order and Grant conducted the surrender allowing for all honors to the defeated army which led to the other generals also ignoring that order and following Lee's lead. All or most of these actions occurred in that fateful month.
The issue with any historical speculation is that it's just that - speculation. Each time there is a guess as to what might have happened, you can say "or not." Yet Winik does a pretty good job of presenting a good argument that may not sway you completely to all his conclusions but does have enough strength to make you think about it. If you like history at all, this one is worth your time.