According to the passage, the formation of a national interest serves what function in the classical realist theory of war and peace?

• A. It is a convenience used by theorists to describe national interests where none exist.
• B. It provides the necessary justification for the classical realist view of a continuous global power struggle.
• C. It is less important to the theory than is the idea of the nation as a unitary actor
• D. It is the part of the theory that receives the most criticism from opponents.