Niebuhr identifies two problems with how the U.S. views itself that can lead the country into foreign policy mistakes. The first is the U.S. is blind when it acts in its own interests but instead credits its actions to some higher morality. Niebuhr identifies this problem as being "innocent." The second danger that Niebuhr identifies is the U.S believing that it is a master of its own destiny and that it controls events instead of being subject to them. Not only does Niebuhr identify these problems he predicts that these problems may lead U.S. to launch a "preventive war."
Niebuhr's solution is not for the U.S. to retreat into isolation but to act in the world. However, it must act knowing that are limits to what the U.S. can do but it must act. Hence the U.S. is in an ironic circumstances.
The book was written in 1952 and in places it is definitely dated. It spends a large section of the book comparing the U.S. to the communist system. It is also blind the the tumultuous current running beneath American society in 1952. There is no acknowledgment of the civil rights movement that is about about to get started or the sometimes violent backlash that wold result.
In all humility I do differ with Niebuhr in one respect. I think renunciation of power is in keeping in both the American tradition and Christian teaching. Since George Washington voluntarily giving up power is not an act irresponsibility but an act of protecting the republic from the danger on entrenched power. The Apostle Paul also believes in renouncing power is an important part of Christ's example. I think an engagement with these two traditions would enhance Niebuhr's point.
Reading Niebuhr is always work but putting in the work will give the reader a prophetic insight into the deep seated and long standing contradictions that bedevil U.S. foreign policy. Knowing what the traps are and how they were placed is the first but most important step in finding our way out of this mess.