Pastoralist access and use of common grazing resources in the Horn of Africa increasingly include armed confrontation over diminishing resources and reduced access. This comes about as traditional customary institutions (sets of rules) for commons management become compromised due to the presence of outside influences and actors which significantly change both resource availability, and conceptions about who is subject to traditional rules governing commons -particularly rules associated with exclusion. At the same time a combination of local knowledge regarding what happens to open access commons (degradation), a reluctance to give up control of commons and associated ways of life, and armed conflict as a viable alternative for exclusion rules, provide for combative situations and large costs. While a great deal of valuable work has been accomplished regarding the derivation of effective institutions to better manage commons, situations of armed conflict can seem particularly distant from effective rule-making, because few institutions can endure the stresses of armed conflict. Recent developments in Ethiopia however suggest an unexpected proximity between armed confrontation and the prospect for commons management rule-making. With examples from the Afar, Somali and Karamojong Cluster pastoralists, this paper examines the ingredients for rule-making in combative commons situations. Specific coincident forms of state recognition, donor flexibility, perceptions of the cost of conflict, and the local to international reaction to these, are examined for their utility and limitations in the provision of a facilitating context for institution derivation for commons management.