Recent historians have highlighted the importance of the web of illicit commercial transactions which connected competing imperial networks to create an integrated Atlantic economy but have paid little attention to how co-operation worked across borders. Of necessity, participants acted without the legal institutions which are often afforded a central role in narratives of modernization. In the case of Jamaica, a hub of illicit trade, most merchants found it difficult to survive in this high-risk environment but members of the Sephardic diaspora, a traditional, communitarian group, had competitive advantages which they exploited with vigour. They did not rely on innate attributes of kinship, ethnicity, or religion. They closed entry and built on a favourable historical and geographical legacy to cultivate attributes which maintained high levels of social discipline with credible rewards and punishments which were reinforced by their outsider status. Their competitive advantages did stimulate retaliation but also allowed the Sephardim to combine with the Christian elite to capture rent-seeking opportunities. Far from falling away as modernization gained pace, the Sephardic diaspora survived and flourished by constructing the strong private-order institutions needed in large swathes of the economy where neither impersonal corporations, nor state enforcement mechanisms, were able to manage risk.