Illegal armed agents try to replace the state both in the monopoly of violence and in the protection of civilian population. We pretend to show that this objective is achieved if armed agents build alliances with groups from the civilian population. How to build this type of alliances? We propose a formal exercise, represented by a game, where an armed agent and a civilian one update their decisions concerning the relevance of already established alliances. Necessary and sufficient conditions for stability of alliances are derived from the results of our model.
