This article assesses why the French and US banks Paribas and Speyers underwrote a series of loans to revolutionary Mexico in 1912 and 1913, when the state was in the process of collapsing. This is a case of a war debt that failed to prevent the borrowing government from suspending payments and subsequently falling. Based on unpublished primary documents, the article shows that the 1913 loan involved a conflict of interest. The credit delayed a default and sustained the price of Mexican securities while Paribas, its main underwriter, was liquidating its Mexican portfolio. Evidence also suggests the existence of asymmetry of information. Paribas accessed pessimistic but accurate first‐hand information on Mexico, while the public read over‐optimistic press reports. Paribas forced the government to sell the bonds on the primary market at a price that was low, controlling for publicly available data. It subsequently sold the bonds at a margin on the secondary market. An additional reason for the lending is the Nacional railway, a state‐owned company that used a share of the funds to pay its debt. More exposed to Mexico than Paribas, the small and internationalized Speyers held the bad bonds it had underwritten.