To understand North Korean strategy today, we must first understand the implications of its geography. Korea is a peninsula jutting southward from Manchuria. The waves of the Yellow Sea break on its western shores, and the waves of the Sea of Japan roll in on its eastern flank. It shares a 30-mile-wide border with Russia, its northeastern border about 70 miles from Vladivostok, Russia’s major eastern port. The southeast corner of Korea juts to within 100 miles of Japan to its south, and the peninsula’s southwest corner angles westward only about 300 miles from Shanghai. In hostile hands, Korea can threaten Japan’s access to the East China Sea and the Pacific from the Sea of Japan. Korea can also potentially interfere with China’s access to the Yellow Sea and potentially to Shanghai.
Japan and China have invaded the Korean Peninsula on several occasions. Its geographical position and size relative to Japan and China made these incursions inevitable. From the Chinese point of view, Korea served as Japan’s axis of advance in China. From Japan’s point of view, if a hostile power were to hold Korea and thereby gain access to the Sea of Japan, it could threaten maritime trade and open the door to invasions of the home islands from the west and the east. When the peninsula was in Japanese hands, Manchuria and the Russian maritime regions, including Vladivostok, were threatened.