istorical IR scholarship increasingly treats the second half of the nineteenth century as a time of transformation. Growing “interaction capacity” spurred new patterns of international organization and international law amidst inter-imperial cooperation and competition. Though it has received little attention in Historical IR, Mexico was at the centre of these occurrences – not only as a victim of imperial aggression but an active proponent of alternative visions of liberal and republican international order. From 1859 to 1867, the country saw a major debt crisis and a related intervention. It defeated an attempt by a leading power, France, to reinstate monarchical governance in the Americas. It then expanded liberal commercial ties with the world economy. Mexican responses – armed, diplomatic, and legal – were profoundly shaped by the leading political figure, President Benito Juárez. Juárez came from a rural and indigenous background before scaling the heights of power. Though recognized as a committed republican, Juárez’s internationalism has been overlooked. He adapted many liberal ideas that shaped later British and U.S.-led orders, but he did so in opposition to imperial expansion. This paper explores Juárez’s internationalist thought and the implications of his leadership on the development on nineteenth international order.