National leaders often worry that civil wars might spread, but also seem to have little grasp on which civil wars will in fact draw in other states. An ability to understand which civil wars are most likely to draw in outside powers and when this is likely to happen has important policy implications as well as simply answering a scholarly question. Joining the Fray takes existing explanations about which outside states are likely to intervene militarily in civil wars and adds to them explanations about when states join and why. Building on his earlier volume, Is this a Private Fight or Can Anybody Join?, Zachary C. Shirkey looks at how the decision to join a civil war can be intuitively understood as follows: given that remaining neutral was wise when a war began something must change in order for a country to change its beliefs about the benefits of fighting and join the war. This book studies what these changes are, focusing in particular on revealed information and commitment problems.