There are some thirty ongoing civil wars – Syria, Afghanistan, and Iraq among the high-profile cases – with the average duration of conflict increasing over the past twenty years. Yet foreign-policy practitioners and scholars disagree on the risk that high levels of intrastate violence pose to major powers and global stability; they also disagree on the extent to which external powers can influence the trajectories of these conflicts or improve governance in areas affected by civil war. Part of an eighteen-month Academy project on Civil Wars, Violence, and International Responses, the essays in the Fall 2017 issue of Dædalus describe the causative factors of and responses to civil wars in the modern era.