Aside from academics, activists such as Myles Horton and Martin Luther King Jr., and numerous politicians have also cited his influence on their thought,[31][32][33][34] including Hillary Clinton, Hubert Humphrey, and Dean Acheson, as well as presidents Barack Obama[35][36] and Jimmy Carter.

The Institute on Religion and Democracy, a conservative think tank founded in 1981, has adopted Niebuhr's concept of Christian realism on their social and political approaches.

The increase reflected his ability to reach people outside the German-American community and among the growing population attracted to jobs in the booming automobile industry.

In the early 1900s Detroit became the fourth-largest city in the country, attracting many black and white migrants from the rural South, as well as Jewish and Catholic people from eastern and southern Europe.

Niebuhr spoke out publicly against the Klan to his congregation,[52] describing them as "one of the worst specific social phenomena which the religious pride of a people has ever developed".

Niebuhr repeatedly stressed the need to be loyal to America, and won an audience in national magazines for his appeals to the German Americans to be patriotic.

[55] Several attempts have been made to explicate the origins of Niebuhr's sympathies from the 1920s to working-class and labor issues as documented by his biographer Richard W.

[59]The historian Ronald H. Stone thinks that Niebuhr never talked to the assembly line workers (many of his parishioners were skilled craftsmen) but projected feelings onto them after discussions with Samuel Marquis.

According to his biographer, the historian Richard Wightman Fox, Niebuhr understood that "Christians needed the leaven of pure Hebraism to counteract the Hellenism to which they were prone".

The main supporters of the fellowship in the early days included Eduard Heimann, Sherwood Eddy, Paul Tillich, and Rose Terlin.

[65] In the book Moral Man and Immoral Society (1932), Niebuhr strongly criticized Dewey's philosophy, although his own ideas were still intellectually rudimentary.

[67]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.

[71] Within the framework of Christian realism, Niebuhr became a supporter of American action in the Second World War, anti-communism, and the development of nuclear weapons.

[75] Niebuhr debated Charles Clayton Morrison, editor of The Christian Century magazine, about America's entry into World War II.

Morrison and his pacifistic followers maintained that America's role should be strictly neutral and part of a negotiated peace only, while Niebuhr claimed himself to be a realist, who opposed the use of political power to attain moral ends.

With his publication of Moral Man and Immoral Society (1932), Niebuhr broke ranks with The Christian Century and supported interventionism and power politics.

Arthur M. Schlesinger Jr.[29] explained Niebuhr's influence: Traditionally, the idea of the frailty of man led to the demand for obedience to ordained authority.

[77]After Joseph Stalin signed the Molotov–Ribbentrop Pact with Adolf Hitler in August 1939, Niebuhr severed his past ties with any fellow-traveler organization having any known Communist leanings.

His ideas influenced George Kennan, Hans Morgenthau, Arthur M. Schlesinger Jr., and other realists during the Cold War on the need to contain Communist expansion.

[78]In the 1950s, Niebuhr described Senator Joseph McCarthy as a force of evil, not so much for attacking civil liberties, as for being ineffective in rooting out Communists and their sympathizers.

[83] Niebuhr preached that: ... it was Protestantism that gave birth to the Ku Klux Klan, one of the worst specific social phenomena which the religious pride and prejudice of peoples has ever developed. ...

I hope there will be a massive demonstration of all the citizens with conscience in favor of the elemental human rights of voting and freedom of assembly" (Niebuhr, March 19, 1965).

"[88][incomplete short citation] Of his country's intervention in Vietnam, Niebuhr admitted: "For the first time I fear I am ashamed of our beloved nation.

Unlike other Christian Zionists, Niebuhr's support of Zionism was practical, not theological, and not rooted in fulfillment of Biblical prophesy nor anticipation of the End-of-Days.

His reading of American history based on this notion, though from the Christian perspective, is so rooted in historical events that readers who do not share his religious views can be led to the same conclusion.

[95] Niebuhr exerted a significant influence upon mainline Protestant clergy in the years immediately following World War II, much of it in concord with the neo-orthodox and the related movements.

[citation needed] The historian Arthur M. Schlesinger Jr. in the late twentieth century described the legacy of Niebuhr as being contested between American liberals and conservatives, both of whom wanted to claim him.

[98] Slate magazine columnist Fred Kaplan characterized Obama's 2009 Nobel Peace Prize acceptance speech as a "faithful reflection" of Niebuhr.

[99] Kenneth Waltz's seminal work on international relations theory, Man, the State, and War, includes many references to Niebuhr's thought.

He talked rapidly and (because he disliked to wear spectacles for his far-sightedness) without notes; yet he was adroit at building logical climaxes and in communicating a sense of passionate involvement in what he was saying.