From The New Republic:
Early in January 1939, the precocious German theologian Dietrich Bonhoeffer, age thirty-two, learned that all males in his age cohort had been ordered to register with the military. A dedicated opponent of the Nazi regime, he might have responded by declaring himself a conscientious objector, but there were two problems with such a course of action. The first was that Bonhoeffer, although pacifist by inclination, was not opposed to violence under all conditions; and he would later play an active role in the conspiracy led by German generals to assassinate Hitler. The second was that his fame in the Confessing Church (more on this below) might encourage other religious leaders critical of the regime to do the same, thereby bringing them under greater suspicion and undermining their efforts to prove that Nazi policies, and especially their rapidly intensifying Jew-hatred, were contrary to the teachings of Jesus Christ.
The solution was provided by America’s most illustrious theologian, Reinhold Niebuhr. Nine years earlier, Bonhoeffer had spent a year in the United States as a free-floating exchange student at Union Theological Seminary, arriving not long after Niebuhr had moved there from Detroit. He had made such a positive impression on Union’s faculty that Niebuhr jumped at the opportunity to bring him back. If we fail to offer him a job, he told Union’s president, Henry Sloane Coffin, Bonhoeffer will wind up in a concentration camp. This was not the stuff of run-of-the-mill letters of recommendation. Union extended the offer. Grateful to have a way out of his dilemma, Bonhoeffer booked passage, and in June 1939 found himself safe in America.
Safe, but unhappy.
More here.