The Democratic People's Republic of Korea, or North Korea, lies on a peninsula extending outward from northeast Asia. The country borders China and Russia to the north, the Republic of Korea to the south, and Japan across the sea to the east. North Korea's primary geographic challenge is securing its northern and southern borders from the threat of its much larger regional neighbors. The Kaema Plateau and Hamgyong Mountains comprise much of the northern border region, providing a strong but not unbreachable geographic barrier. The Taebaeck Mountains run along the east coast, limiting the potential for invasion from the sea. Since the time of earlier North Korean kingdoms including Koguryo, The Dandong-Sinuiju gap across the Yalu River in the northwest and the wide Imjin-Han river valley in the south leave the country vulnerable, particularly with the lack of geographic barriers along the north-south axis. North Korea's mountains do provide ample hydropower, and the country also has numerous natural mineral resources and coal, but its terrain and climate limit agricultural activity. Given its larger neighbors, North Korea has two core imperatives. It must secure its southern and northern borders via political accommodation, defensive lines or outward expansion, and it must engender a strong sense of national unity and exploit differences among its neighbors to balance external political pressure. From the launching of the Korean War to the heavily fortified DMZ, from the exploitation of relations between China and Russia to the development of a nuclear deterrent, North Korea's actions in many ways are shaped by similar constraints and pressures as felt by its predecessor kingdoms due to its location and geography.