This article builds on the recent willingness among British, Canadian, and imperial historians to question older national histories, and to re-examine how the divergent societies, economies, and polities of the empire once interacted in a wider ‘British world’. It argues that the press acted as a key mechanism for the transmission of political ideas through the permeable internal boundaries of empire. This is demonstrated through analysis of contemporary debate over the Canadian–American reciprocity proposals of 1911. This controversy provided an opportunity for political groups in Britain and Canada to use the press to forge alliances with each other and work together on a specific issue. Two key forces made this possible. In Britain, constructive imperialists had since 1903 sought to rally Dominion support for tariff reform, initially with limited success. In Canada, neither western farmers nor eastern manufacturers seemed interested in imperial preference. It was the reciprocity proposals that changed the situation, providing the second driving force. Canadian manufacturing interests, seeking to prevent the lowering of tariff barriers against United States rivals, began to court British constructive imperialists. As a result political conflict was reshaped both in colony and metropole.