The American Protestant theological and reform movement of roughly 1880 to 1920 that insisted Christianity is concerned not only with personal salvation but with the redemption of social structures — and that the industrial capitalism, urban poverty, child labor, slum housing, and political corruption of the Gilded Age were not regrettable circumstances within which the church operated but were the proper subject of Christian moral and political witness. The movement's central figure was the Baptist pastor and theologian Walter Rauschenbusch, whose Christianity and the Social Crisis (1907), Christianizing the Social Order (1912), and A Theology for the Social Gospel (1917) gave it its theological articulation. Washington Gladden, Josiah Strong, and the YMCA leader John R. Mott were among its other public faces.
Theologically, the Social Gospel read the Kingdom of God less as a future heavenly state and more as an immanent project — to be approximated, however partially, through the reform of human institutions in light of the ethical teachings of Jesus, especially the Sermon on the Mount. The movement was unembarrassed by political engagement; it supported the labor movement, settlement-house work (with which Jane Addams is associated), tenement reform, prohibition, public health initiatives, and what would eventually become the institutional architecture of the American welfare state.
The Social Gospel's influence outran the movement itself. Reinhold Niebuhr began as a Social Gospeler and spent his subsequent career arguing against what he came to see as its sentimental optimism about human nature and historical progress; Moral Man and Immoral Society (1932) is in large part a critique of his Social Gospel inheritance. Martin Luther King Jr. read Rauschenbusch closely as a divinity student and acknowledged him as a major influence on his understanding of Christian social responsibility. The line from Social Gospel through King to contemporary American Christian social-justice movements is direct, even where the lineage is no longer named.