Based off of the events in america such as Ferguson and Baltimore, i feel this will be a racial war, these events are going to spark it, this is mostly how it will go down. So if your white or black get ready the next acw will be a racial one,
It will be fought between those who live for telling others how to live and those who are sick and tired of it and want to be left alone to live as they choose. A very political war, not about race or religion, although both might get dragged into it by self-serving interests..
I think that, hypothetically, if there is going to be another American Civil War, it will almost surely be the culmination of "Class Warfare." The majority of disputes in the past few years have been between upper class and working class demographics. I firmly believe that the media has painted many of these disputes with the brush of racial inequality to stifle the concept of class warfare.
IF there were to be another American civil war, I think that it would be between the socialists that are trending towards fascists and the conservatives, that are trending towards libertarian. Basically the two ideologies that are opposites in what they believe the role of government is. Some people want the government bigger and so they government has been growing in size and scope, when others want extremely limited government that just protects rights. Eventually the government will grow to big and have too much power and will infringe the rights of the citizens until one day one side can't take it anymore and revolts.