Examining the social and intellectual collision of the American reform tradition with immigrant Marxism during the Reconstruction era, this text charts the rise and fall of the International Workingman's Association (IWA). The IWA's attraction to American reformers (including those involved in women's rights), the effect they had on the American Left, and the reasons behind their ultimate purging from the IWA by more orthodox Marxists are all examined. The ideology and activities of the Yankee Internationalists are also explored, as the author traces the evolution of antebullum American reformers' thinking on questions such as wage labour. Linked to this is the exposition and analysis of how American reformers' priorities of racial and sexual equality clashed with their Marxist partners' strategy of infiltrating the trade union movement. It is argued that, ultimately, Marxist demands for party discipline and ideological unity proved incompatible with the Yankees' innate republicanism. This resulted in the expulsion of the Yankees from the IWA in 1871 and the separation of Marxism from the American reform tradition.