Before revision: We investigate the role of networks of military alliances in preventing or encouraging wars between groups of countries. A country is vulnerable to attack if some allied group of countries can defeat the defending country and its (remaining) allies based on their collective military strengths. We show that there do not exist any networks which contain no vulnerable countries and that are stable against the pairwise addition of a new alliance as well as against the unilateral deletion of any existing alliance .
After revision: We investigate the role of networks of military alliances in preventing (multilateral) interstate wars. We first show that, in the absence of international trade, no network of alliances is peaceful and stable .