This article reviews the economic history of war, a literature that comes not just from economics or from history but from political science and sociology as well. We first cover the review scholarship on the pre-modern period, especially the formation of European nation states and conflicts. It seems clear that Europeans emerged from this period with a comparative advantage in violence, through technological innovations and repeated warfare. Fiscal innovation and the expansion of state's capacity to tax were a key part of the process. The conflicts during the French Revolution and the Napoleonic period then changed the nature of warfare and ushered in an era of total war and industrialization. Then came the world wars, the period that economic historians have devoted more attention to than any other. New data and scholarship has shown the mechanics of mobilization and highlighted the importance of resources in deciding these conflicts. By contrast, the subsequent Cold War years have been relatively sparsely studied, at least from the perspective of conflicts or military spending. Given the availability of new data and the opening of many archives, it is highly likely that this state of affairs will change in the near future, and researchers may also shift to questions that arise outside of Europe and western democracies. Overall, economic historians studying war have had an impact on related long-run phenomena such as state formation, empires, and the growth of democracy. Cliometrics is well suited to the study of such topics, given the new panel and time series techniques, the rapid development of computing power, and the many new online databases.