Labor had made strides during the Progressive Era that preceded World War I, and in many cases had become more radical. Many unions took strident anti-war positions prior to US involvement in the conflict. Yet repressive measures by the federal government combined with higher wages driven by the demands of a wartime economy to silence union protests. While some radicals, most notably the Industrial Workers of the World, refused to support the war, the mainstream American Federation of Labor, led by Samuel Gompers, agreed not to strike during the war in return for significant gains. Other non-affiliated unions followed suit. Unions thus won recognition through participation in the war effort. But when the war ended, they quickly lost many of the gains they had made as the federal government under Harding and Coolidge was highly unsympathetic to their cause. Many of the collective bargaining rights they won during the war were lost, and were not restored until the Wagner Act, part of Franklin Roosevelt's New Deal in the 1930s.
Women did not participate in American auxilliary forces in large numbers as they did in the Second World War, but they served important roles in the conflict. Aside from the obvious work they did to keep their homes intact in the absence of their husbands, they also joined the workforce out of necessity in large numbers. While they did not work in heavy industry for the most part, they did administrative work that had previously been denied them, and their role as breadwinners caused many women to call into question Victorian notions of separate spheres and the behaviors and expectations that were associated with them. It was in part the important roles occupied by women during the war, as well as suffrage advocates' skillful appeals to Woodrow Wilson's democratic rhetoric throughout the war, that led to popular support for the Nineteenth Amendment, which finally guaranteed the vote to all women.
African-Americans served in the armed forces in large numbers, and returned home to experience very few substantial reforms, and indeed suffered a wave of lynching in the South that rivaled any during the dying days of Reconstruction. The war did contribute to one of the seminal moments in African-American history, however. Lured by the promise of increased economic opportunities in wartime industries, hundreds of thousands of black families moved to northern cities like Detroit and never returned to the South. While still facing resentment from white workers, and de facto segregation in northern cities, blacks who moved north found economic opportunities they never could have experienced in the Jim Crow South. This enormous demographic shift has become known to historians as the Great Migration, and it was a direct effect of the First World War.