Answer:
It prevents Moscow from doing any fighting on its eastern borders
Step-by-step explanation:
Under the Treaty of Mutual Cooperation and Security between the United States and Japan, the United States is obliged to protect Japan in close cooperation with the Japan Self-Defense Forces for maritime defense, ballistic missile defense, domestic air control, communications security (COMSEC) and disaster response.
After the defeat of Japan in World War II, the United States led the Allies in the occupation and rehabilitation of the Japanese state. Between 1945 and 1952, the U.S. occupying forces, led by General Douglas A. MacArthur, enacted widespread military, political, economic, and social reforms.