In light of the actions of Hitler and the Japanese, his "Christian Realism" theory forced him to re-examine many of his previous views on the world. Niebuhr severed all socialist connections after Hitler and Stalin signed a non-aggression pact in 1939 and was a staunch supporter of America's entry into the war. He viewed sin as part of the world, felt it was more important to have justice in the world than universal love, felt the pacifist movement was unable to stop sin in the world, and that power could be balanced by power. He criticized the members of the pacifist movement for using intellectual arguments to respond to real threats. He claimed that the pacifist and non-interventionists "…shrouded the conflict in an ambiguity that operatively established a 'moral equivalency' between Nazism and the admitted flawed democracies." (Bullert) the United States, Allies, and other democracies represented the hope for the human race, that they would counter the evils of the world. He proposed realistic answers for the complicated issues confronting the world at that time. After the war. Reinhold Niebuhr focused his attention on ethical meaning of American History. His 1952 book "The Irony of American History" took a hard, ethical look at the history of the United States. His interpretation of American history determined that liberal democracy was a better method of creating common good than Marxism, and that "…on the whole, [American government] is expected to gain its ends by moral attraction and limitation." (Berke) He criticized "American Idealism" as either pro-war imperialism, or anti-war non-interventionism. The pro-war crowd, he argued, viewed power as a virtue, while the anti-war movement was embarrassed by power. Niebuhr concluded that there were two major ironies concerning the United States; that the United States has acquired a great deal of power without actively seeking it, and that possessing such power come with it global responsibilities which limit the United States ability to control it's own destiny. (Berke)

It may seem strange that a person who spent his entire life working of the good of society would endorse segregation, but that is exactly what Reinhold Niebuhr did. Believing that the solutions to social evils should evolve in society, he viewed segregation as a pragmatic solution to a complicated problem, that forced integration would cause...

However, by the late 1960's the realities of the social situation in America forced him to again re-evaluate some of his basic beliefs. He came to the conclusion that society was never going to be able to actually accomplish "separate but equal," and that forced integration was the only way to alleviate social ills. (Fox) He also opposed American involvement in Vietnam claiming that the United States was acting in a "power is virtue" way ultimately which would lead to disaster.
Reinhold Niebuhr has been one of the 20th century's most influential thinkers and his influence can be seen throughout American theological thought, politics, and social causes. His "neo-orthodoxy" has become the absorbed into modern Protestant theological thought, while his "Christian realism" has become the basis of political discourse in the nation. The "Catholic Liberal Theology" of Central and South America can trace it's roots back to Niebuhr's teachings, as well as social movements such as Feminism, Gay Rights, and the Ecological Movement. In terms of American politics, both John McCain and Barack Obama took occasion in their 2008 campaigns to associate themselves with the teachings of Niebuhr; as many politicians have done. Although Reinhold Niebuhr died on June 1st, 1971 in Stockbridge, Massachusetts, he lives on through his works and continues to influence American society.