In the 1930s Niebuhr worked out many of his ideas about sin and grace, love and justice, faith and reason, realism and idealism, and the irony and tragedy of history, which established his leadership of the neo-orthodox movement in theology. Influenced strongly by Karl Barth and other dialectical theologians of Europe, he began to emphasize the Bible as a human record of divine self-revelation; it offered for Niebuhr a critical but redemptive reorientation of the understanding of humanity's nature and destiny.