FIGURE 17.1 Union Membership, 1870–1900 Union membership fluctuated widely in the late nineteenth century. After reaching a low point in 1880, the number of union members rebounded after organizing by the Knights of Labor. Membership plummeted in the years after the Haymarket Square incident of 1886 but soared again in the 1890s through the efforts of the American Federation of Labor and western miners. Source: Data from Richard B. Freeman, “Spurts in Union Growth: Defining Moments and Social Processes” (working paper 6012, National Bureau of Economic Research, Cambridge, MA, 1997).