The correct answer is the United Nations.
The North Atlantic Treaty Organization was an alliance formed by the US, Great Britain, France, and several other countries after World War II. However, the goal of this organization was not to spread peace. Rather, it was an alliance that stated that if one country got into a war, all the other countries would support it.
The Peace Corp was a program founded by John F. Kennedy that involves individuals traveling to third world countries to help them improve.
The World Bank is an organization based on giving loans to different countries for projects.
This shows how only the United Nations can be the correct answer.