Why do the Group of Eight (G8) members approve its members’ use of material sanctions in some regional conflicts but military force in others?2 As an informal security institution composed of major democratic powers from North America, Europe and Asia, the G8 has often chosen sanctions, notably on Iran in 1980, Afghanistan in 1980, Sudan in 2004, North Korea in 2006, and Syria in 2011. It has increasingly chosen military force, notably in Iraq in 1990, Kosovo in 1999, the USSR over Afghanistan in 2001, Libya in 2011, and Mali in 2013. Yet the G8’s choice, initiation, commitment, compliance, implementation and effectiveness of both sanctions and force has varied. Force was chosen and used effectively only in the post cold war period, primarily where the target was close to southern Europe. A high relative-capability predominance of G8 members over the target country strongly produces the G8’s choice of force, but a high, direct, deadly threat from the target state to G8 countries does not. Geographic proximity and the connectivity coming from the former colonial relationship between G8 members and the target country only weakly cause the G8 to choose force. Support from the most relevant regional organization – the North Atlantic Treaty Organization – and support from the United Nations in the form of an authorizing UN Security Council or General Assembly resolution have a strong, positive effect on the G8’s choice of force. Accompanying accountability mechanisms from the G8 itself have a variable impact, as leaders’ iteration of the issue at subsequent summits does not increase compliance with G8 commitments on force-related cases, but their foreign ministers’ follow up does to a substantial degree.