Our paper explores the economic conditions that lead third parties to intervene in ongoing internal wars. We develop a formal model that ties together some of the main forces driving the decision to interfere in a civil war, including the economic benefits accruing from the intervention and the potential costs associated with such choice. We predict that third party interventions are most likely in civil conflicts where the country at war harbors a profitable industry as a consequence of its high levels of peace-time production and state strength, while the opposition forces’ strength reduces the likelihood of intervention. We also present novel empirical results on the role of valuable goods, i.e. oil, in prompting third party military intervention in contexts of high state stability, by using a dataset on intrastate conflicts on the period 1960-1999.