Author of many books on American labor and politics, Lens shows in this survey of labor from the 1870's through the 1930's a strong sensitivity to the molecular development of mass movements, the inchoate motion that takes place before the political battle erupts. Lens is aware that workers' motivation and their tactical capacity to expand the strike or civil liberties battle depends not so much on their own immediate material circumstances such as wages and working conditions but on the broad political climate of the times. He accurately identifies the strength of the IWW ""Wobblies"" with reference to their slogan -- ""An injury to one is an injury to all""; he locates the 1934 mass strikes of Toledo, Minneapolis and San Francisco as the turning point of the '30's, rather than the subsequent consolidation of the CIO; and he highlights the leading role played by socialists from the American Workingman's Party (A. J. Muste's group), the Communist League, and the Communist Party. In a wholly sympathetic vein Lens spans the Molly Maguires, the 1877 mass strikes, the Pullman struggle, Haymarket and the eight-hour day, the meatpacking and steel drives for unionization. Lens, who says he is writing to edify American youth, believes that today ""labor war"" is no longer inevitable unless Nixon imposes ""political regimentation."" This is a solid history, more conceptually fertile than most.