This dissertation examines the question: To what extent does the international news media influence the outcome of interstate wars? It considers the longstanding charge that media reports of public debates about foreign policy provide aid and comfort to the enemy. New theory is proposed that addresses this policy problem facing democracies, and also addresses gaps in the theoretical literature on the causes of war. The theory advanced in this dissertation is that the presence of the international news media influences the outcome of wars by providing an additional channel through which information about leaders cost sensitivity is revealed and by reciprocally influencing the beliefs and behavior of leaders and their foreign adversaries in the conduct of wars. Novel variables representing major phases in the emergence of the international news media are defined. Original research is conducted using primary and secondary sources to characterize the media by year in individual states. The novel media variables are combined with variables from other studies to create a dataset spanning 90 interstate wars involving 51 different states from 1823 through 1990. Hypotheses based on the theory are tested using a multinomial logistic regression model. The results of this study partially support the theory in that the type of media in a war initiator state is strongly and significantly associated with a higher probability of winning. Unexpected findings regarding the influence of media speed on the probability of winning, and a failure to find a relationship between media and the probability of losing require further investigation. Overall, however, the presence of the international news media appears to influence the outcome of interstate wars. The results have important implications for future theoretical research as well as for policy choices regarding the proper role of domestic debates and media reporting thereof. Additional research is required to confirm the findings, examine the unexpected findings, and to examine the relevance of the findings in other eras and other phases of war. Deeply rooted assumptions within society that media reporting on wars conflicts with national security interests must be revisited as part of an examination of policy implications of the findings.