"Since wars begin in the minds of men, it is in the minds of men that the defences of peace must be constructed." This observation can be found in the Constitution of which one of the following Organs of the United Nations?

The quoted observation appears in the Preamble to the Constitution of the United Nations Educational, Scientific and Cultural Organization (UNESCO), which was adopted in November 1945. The full text of the Preamble begins with this famous statement, which reflects UNESCO's mission to build peace through international cooperation in education, science, culture, and communication. This idea is foundational to UNESCO's purpose. Hence, UNESCO is the correct answer.