Divided since 1948, myriad factors affect the security situation on the Korean Peninsula. Because North Korea possesses nuclear weapons, the security situation in its area is of paramount importance.
One important factor is the attitude of the two great powers that border North Korea. These two nations, China and Russia, supported North Korea during the Korean War (1950–1953), and they continue to have relatively cordial relations with Pyongyang today. North Korea is especially reliant on China for economic assistance. Moscow and Beijing do not want another war on the Korean Peninsula, so they sometimes act to reign in North Korea's aggressive tendencies. Also, China does not want to see a unified, pro-American Korea.
The relationship between the United States and the two regimes on the Korean Peninsula is also important. Since the end of the Korean War, American presidents avoided direct contact with North Korea's leaders. But this policy ended under president Donald Trump. Trump has met Kim Jong-un, leader of North Korea, on three separate occasions. Although the two men seem to have a friendly relationship, North Korea continues to destabilize its region by testing missiles and threatening its neighbors—including Japan. South Korea and the US are firm military allies, and thousands of US troops are stationed there.
The economic situation in North Korea is also relevant to the security situation. North Korea is an extremely poor country, and it devotes most of its limited resources to its military. South Korea, eager to stabilize the Peninsula, has been providing economic assistance intermittently for decades. But many South Korean leaders believe that that aid has largely come to naught.