This departure from his peers evolved into a movement known as Christian realism. Niebuhr is widely considered to have been its primary advocate. Niebuhr supported the Allies during the Second World War and argued for the engagement of the United States in the war. As a writer popular in both the secular and the religious arena and a professor at the Union Theological Seminary, he was very influential both in the United States and abroad. While many clergy proclaimed themselves pacifists because of their World War I experiences, Niebuhr declared that a victory by Germany and Japan would threaten Christianity. He renounced his socialist connections and beliefs and resigned from the pacifist Fellowship of Reconciliation. He based his arguments on the Protestant beliefs that sin is part of the world, that justice must take precedence over love, and that pacifism is a symbolic portrayal of absolute love but cannot prevent sin. Although his opponents did not portray him favorably, Niebuhr's exchanges with them on the issue helped him mature intellectually.