I believe Trump convinced Chinese Premier Xi at Key Largo that it is in China’s best interest to bring down the North Korean regime and to reunite Korea, and they agreed to a plan to do that.  China will first amass an army of soldiers along the China-North Korean border to prevent Korean refugees from crossing into China.  China will then cut off all aid to North Korea while the U.S. and South Korea impose a naval blockade of North Korea to prevent ships from entering or leaving North Korea.  It might take a year or two before North Korea collapses, but it is the only way to make it happen short of war without the outside aid North Korea now receives.  Yes, innocent North Koreans may suffer, but probably no more than they suffer now.