B. It underscores the need for mutual cooperation and action from both the United States and other nations, thereby emphasizing a balanced approach to global issues.
The repetition of the phrase "Let both sides" in Kennedy's Inaugural Address serves to highlight the importance of collaboration and shared responsibility in addressing global challenges. It emphasizes that resolution and progress require effort from all parties involved, reinforcing the idea that diplomacy and cooperation are essential for peace and stability in the world. This approach enhances the effectiveness of his message by promoting a unified, collaborative stance in international relations.