The graphic is also something of a historical trailer.
To begin with, it would not look like the first American Civil War, which was essentially a war between two regions of the country with different economic interests. The divide created two separate countries, both initially contiguous, intact, and relatively homogeneous. The lines of demarcation now are only somewhat regional, and tend to correspond to differences between urban and rural populations, as well as differences of race and class. A second American Civil War would be much more similar to the Spanish Civil War, with the leftists dominating the cities and conservatives controlling the countryside. Conflicts of this nature, with enemies mixed geographically, are a formula for spontaneous mass bloodletting. India-Pakistan during the 1947 partition comes to mind as another modern example. Given an absence of legitimate government and the friction of proximity, ordinary people can be moved to settle grievances by killing one another without the need for governments to egg them on.