The Kim Jongs promise to be good, then break the agreement, run out of cash, make promises to be good again... then break them again... it is the family M.O.
The UN sanctions and the additional pressure on China by Tillerson and Trump to cut him off and block petrol imports did work, (the junior high style tweets are only to impress the Fox news crowd) HOWEVER this is not the first time there is promises let's wait and see if he actually keeps them long term before shouting viiiiiiictory
