Spinsters, Gamblers, and Friedrich Engels: The Social Worlds of Money and Expansionism in Argentina, 1860s–1900sAbstract: This article explores the social aspects of steam-age expansionism in Argentina by illuminating two groups often overlooked in standard histories of capitalist investment: the European investors who supplied the funds and the local workers who made capital projects realities. Focusing on the 1860s to the early 1900s, the first section draws on British company records to identify the actors who enabled informal empire. These include so-called gentlemanly capitalists but also investors from more varied backgrounds, among them a significant number of women. The second section examines capital-fueled growth from the vantage of working-class sectors, observing how a mobile, multiracial workforce transformed investment flows into railways and other infrastructure. Although laborers did not control transborder movements of capital, their earning of wages was not just about survival: within the limited possibilities available to them, they created their own ways of courting fortune and multiplying money.