US softens its stance against North Korea after China and Russia conduct joint anti-missile exercises.

https://sg.news.yahoo.com/tillerson-softens-us-stance-possible-talks-nkorea-222702752.html

http://www.chinaeconomicreview.com/china-russia-conduct-joint-anti-missile-exercises

China and Russia have sent a strong message to the USA not to act unilaterally through the joint anti-missile exercises which can also be used to shoot down fighter planes flying in NK's sky.

The USA knows that it cannot defeat China & Russia in the Peninsular war.  Therefore, the USA softens its stance and is willing to resolve the issue through diplomatic talk now.