ABSTRACTDuring the 1860s Cape Breton Island’s Sydney coalfield, at the northeastern tip of Nova Scotia, experienced dramatic economic expansion. Historical interpretation of this understudied coal boom has emphasised the transition towards a liberal era of competition and growing dependence upon American capital and markets. This article presents a revised interpretation, and reflects a renewed engagement with empire in the writing of the history of Canadian capitalism. Drawing upon the work of James Belich and John Darwin, it locates this coal boom in an evolving and expanding ‘Angloworld’ and ‘British world-system,’ and demonstrates how the Sydney coalfield was shaped by the social and economic configurations that developed in the region under the British Empire. During this period, established colonial elites captured coal property and sought to integrate Cape Breton coal into the Atlantic economy in which their region had historically operated. They treated coal as a new commodity to trade and profit from, but coal mining required the mobilisation of credit and infrastructure expenditures that exceeded what was typically required to participate in the region’s traditional staples trades. Large fixed investments engendered economic and political commitments that spurred growth even under highly volatile circumstances, as promotion and speculation drove growth from the supply side and attracted London capital. Overcapacity, ruinous competition, and social crisis eventually resulted, as the Atlantic economy that gave rise to the boom fell apart. This episode reveals the operation of colonial networks and an ‘empire effect’ that produced a distinctive pattern of development on the Sydney coalfield whose legacy would be lasting.