Within the global Spanish empire of the early modern era, the signifier portugués carried an expansive variety of associations. It could mean, depending on the observer, being either Spanish or foreign, Catholic or Jewish, useful or deleterious, loyal or treasonous. In Strangers and Kinsmen, historian Brian Hamm argues that discursive debates about what it meant to be "Portuguese," to which Spaniards and Portuguese alike contributed, opened a wide range of Lusitanian potentialities that could either accelerate or hinder Portuguese integration within the Spanish Atlantic world. As a result, uncertainty followed Portuguese immigrants across the Atlantic and plagued Spanish officials who had to decide how to respond to an ever-increasing number of Portuguese arrivals. To find convincing answers, as Hamm shows, the Portuguese and Spanish looked to public behavior and personal reputation. The most convincing proof of Portuguese loyalty, piety, and utility came from consistent performances of virtuous actions by the Portuguese themselves. At the same time, public behaviors deemed suspicious, heretical, or treasonous could have the opposite effect, confirming in the minds of Spanish observers that the Portuguese were dangerous foreigners, potentially engaged in conspiratorial activities, who should be excluded. Because of the interpretative significance placed on public patterns of behavior, Portuguese immigrants gained significant opportunities to negotiate a more secure and accepted place in colonial society.

Strangers and Kinsmen recovers the complexity and heterogeneity of Lusitanian immigration to the early modern Spanish Indies. Prioritizing Portuguese immigrants frequently overlooked in previous studies, including pilots, soldiers, priests, and spies, Hamm's detailed analysis expands scholarly understanding of the thousands of Portuguese who collectively strengthened and threatened Spanish imperialism from within one of the most geopolitically vital regions of the world.