We think we know civil war when we see it. Yet ideas of what it is, and isn't, have a long and contested history. Defining the term is acutely political, for ideas about what makes a war "civil" often depend on whether one is ruler or rebel, victor or vanquished, sufferer or outsider; it can also shape a conflict's outcome, determining whether external powers are involved or stand aside. From the American Revolution to the Iraq war, pivotal decisions have hung on such shifts of perspective. The West's age of civil war may be over, but elsewhere it has exploded – from the Balkans to Rwanda, Burundi, Somalia, Sri Lanka and, most recently, Syria. And the language of civil war has burgeoned as democratic politics has become more violently fought. This book's unique perspective on the roots, dynamics and shaping force of civil war will be essential to our ongoing struggles with this seemingly interminable problem.