This study analyzes the Soviet Union’s strategic interests and policies toward Mongolia, emphasizing Joseph Stalin’s perception of its geopolitical importance. It examines why Mongolia’s independence was a key condition Stalin set at the Yalta Summit for the Soviet declaration of war on Japan. While existing research has explored Soviet-Mongolian relations, this study utilizes newly declassified archival materials from Russia, Mongolia, and Japan to reassess Stalin’s strategic vision and interactions with Mongolian leaders.