This elegantly written history of ideas is a timely reminder that parts of the left were strong advocates of commercial liberalism and thus the conjecture that free trade can make the world more peaceful. Drawing on a rich array of sources, Palen puts key contributions by different thinkers, ranging from Richard Cobden to Karl Marx and Cordell Hull, into the historical context. This helps to understand that the left´s ‘free trade cosmopolitanism’ often reacted to a particular era's militarism, colonialism, and protectionism. The author´s erudition navigates us through two centuries of forgotten, well-remembered, and ongoing debates among dozens of leftist intellectuals (this ancestral gallery includes, from a European perspective, mainstream liberals who would not locate themselves on the left of the political spectrum).  The book does not advance a theory that would assist the reader in understanding the ups and downs of the ‘Pax Economica’ in the intellectual discourse and its political application. This might be a consequence of the neglect to point out the redistributive effects of economic openness and the lack of differentiation between the current and the capital account. While growing trade might make societies peaceful after the compensation of globalization losers, the withdrawal of portfolio investments can destabilize fragile societies, as Joseph Stiglitz has argued. The contributions of this Nobel awardee are missing from Palen´s discussion, as are those of Paul Krugman, Paul Samuelson, Wolfgang Stolper, Jacob Viner, and many influential ‘liberal’ or ‘leftist’ economists who have rigorously highlighted the domestic struggles over the free trade orientation of a country. ‘Pax Economica’ is nevertheless a worthwhile addition to the literature on the liberal peace thesis.