Director Alex Garland is out to prove that you can make a movie about a modern American civil war without getting political. And he wants to do it in an election year. The question is: Why? His new film “Civil War,” which opened in cinemas on Friday, follows an unlikely group of journalists as they make their way from New York to Washington, D.C., as the rebel “Western Forces,” made up of California and Texas, close in on the capital. Two of those journalists — Lee (Kirsten Dunst), a legendary conflict photographer, and Joel (Wagner Moura), a writer — hope to secure the final interview and ima…