This chapter explores the transformation of the world of the American worker wrought by the Great War.Before the war, American industry demanded an endless supply of cheap labor. This imperative structured all aspects of working-class life——labor conditions and pay, home and neighborhood, politics and labor organization, and even its heterogenous racial and national composition. It had brought into being a working class at once within and apart from mainstream America. The economic and political forces unleashed by the Great War made America’s workers both the objects and agents of immense change. With the drastic curtailment of immigration caused by wartime conditions, workers could no longer be viewed as replaceable cogs, mere labor inputs in the production process. Neither could the insularity of their communities be tolerated, for during war, government and industry demanded loyalty, even active allegiance. Yet workers seized on the possibilities presented by the war in a bid to chart their own course. Emerging from this maelstrom was a dramatically different relationship between workers, on one hand, and business and government, on the other, ending the epoch of mass immigration and putting in place the beginnings of a labor system that valued long-term employment and worker loyalty.