War between the US and North Korea is “not unimaginable”, said General Joseph Dunford, Chairman of the Joint Chiefs of Staff of the US Armed Forces. The reason is Pyongyang's nuclear missile program. However, General Dunford admitted, that "anyone who's been alive since the Second World War has never seen the loss of life that could occur if there's a conflict on the Korean Peninsula."
The senior officer of the US Armed Forces knows what he is talking about. The possibility of a military operation against the DPRK was discussed in Washington from the early 1990s, as soon as Pyongyang's nuclear program began. According to forecasts submitted in 1994 to the US President Bill Clinton by the then commander of the US forces in South Korea, General Gary Luck, the total losses of the United States and South Korea could reach almost a million troops, including up to 100,000 killed Americans. The total cost of the war with the DPRK was estimated at 100 billion dollars, and the amount of economic damage to South Korea - more than 1 trillion dollars.  Such losses were unacceptable for the Clinton administration, and it decided to negotiate with Pyongyang.
Today even "pinpoint strikes" on North Korean nuclear missile sites would lead to even more severe consequences. Only one example. On the border of the demilitarized zone (DMZ), which separates the two Korean states, there is South Korean Greater Seoul, a city of about 25 million people. On the opposite side of the DMZ there is the world's most powerful concentration of the North Korean heavy artillery. The artillery shelling of Seoul by the North Koreans is capable of inflicting damage to the South Korean capital, comparable to the use of nuclear weapons.
It is significant, that when Pyongyang threatens its potential enemies with nuclear missile strikes, in each case it is only about response strikes to external aggression against DPRK. By the way, some sober heads in the United States noted this. For example, William Perry, the US Secretary of Defense in the Bill Clinton administration, wrote: "The North Korean leadership is not suicidal; they are not seeking martyrdom. They want to stay in power, and they understand that if they launch a nuclear attack, their country will be destroyed, and they themselves will be killed — it would end the Kim dynasty. Their nuclear arsenal does give them a tenuous hold on power, but only if they do not use it. "
For Pyongyang, the nuclear missile program is a shield for its security, and it will not simply give this shield up. The North Korean leadership knows how the West "thanked" Libyan leader Gaddafi for voluntary renunciation of the nuclear program, and does not want to repeat his fate. Therefore, there is only one way out for the United States and the entire international community - to negotiate with Pyongyang, and to agree specifically, honestly and transparently about security guarantees, first and foremost, for the DPRK and the Republic of Korea, as well as for Russia and China, Japan and the USA. Such guarantees should be durable and convincing enough that no one had any suspicions about them.
North Korea as Trump's Main Foreign Policy Problem
If Trump decides to engage directly with North Korean leaders, however, then Beijing and Moscow might facilitate such outreach as they have long endorsed this approach
The ways to find a compromise on the nuclear issue are not closed. As a starting point for the beginning of political negotiations, one could use the 8 March proposal by the Chinese Foreign Minister Wang Yi, that the DPRK suspends its missile launches and the development of the nuclear program in exchange for the suspension of military exercises by the United States and South Korea. This proposal may be well accepted by Pyongyang - similar ideas were already voiced earlier by the North Korean leadership in January 2015 and January 2016. 
The solution of the nuclear problem of the Korean peninsula is closely connected with the inter-Korean normalization - the development of relations between the DPRK and South Korea. It is necessary to solve both problems simultaneously. And one can only welcome the line of the new South Korean President Mun Zhe Ying on a direct dialogue with Pyongyang and phased solution of the nuclear missile program issue.
The return of the "Korean issue" to the UN agenda can play a positive role as well. Now it is the right time for this. Ban Ki-moon, who was from South Korea, could not be impartial in his approaches to the DPRK, and Pyongyang ignored him emphatically. He completed his tenure as UN Secretary General. His successor, António Guterres, was not previously associated with Korea, and therefore can show a fairly objective and constructive approach to the matter of the inter-Korean settlement.
Gleb Ivashentsov was Ambassador of the Russian Federation to Republic of Korea in 2005-2009
.https://ru.wikipedia.org/wiki/Ракетно-ядерная_программа_КНДР .Пентагон не напал на КНДР, испугавшись потерь. Правда.Ру (20 октября 2006). Проверено 9 мая 2016г.
. ПРЕСС-РЕЛИЗ Посольства Корейской Народно-Демократической Республики в Российской Федерации 15 марта 2016 года www.arirang.ru/archive/edinstvo/2016/Edinstvo.2016.03.pdf