The years 1861 to 1921 witnessed the development of contacts between the labour movements of Britain and the United States. Scottish socialists, trade unionists and social reformers contributed to this activity. Transatlantic labour co-operation began in Scotland in the 1860s when the Civil War in the USA provoked an intense public discussion of American society. This interest was further stimulated by the accounts of emigrants to the republic and, in particular, by the views of Alexander McDonald, leader of the miners' union. The establishment of ties between the mining communities of Scotland and American, via an emigration scheme and through McDonald's lecture tours, inaugurated a period of American influence on the Scottish labour movement. Left-wing reactions in the United States to the growth of capitalism from the 1880s to the First World War furnished sections of this movement with a series of organisational models. Socialist and reform theories, forged in a country which was industrialising at a furious pace, were transmitted to Britain where Scots transformed them for their own purposes. Beginning with the ideas of Henry George, and closely followed by those of the Knights of Labor, these concepts advanced the cause of socialism within the Scottish labour movement. This process culminated with the experiments of the Scottish De Leonists. They instituted the Socialist Labour Party of Great Britain in the image of Daniel De Leon's American SLP and, following the birth in Chicago of the Industrial Workers of the World, brought the theory of industrial unionism to Scotland. De Leonism played an important role in the rise of socialism on Clydeside in the early years of the twentieth century until the Bolshevik revolution in Russia, and the growing mass appeal of the Labour Party, heralded the decline of transatlantic socialist unity.