The kill chain system refers to the Seoul-driven counterattack strategy, which preemptively detects and intercepts missiles and nuclear threats from Pyongyang. Seoul and Washington agreed in October to first strike the DPRK if signs of Pyongyang's nuclear attacks are detected.
Somebody please tell me this is Chinese disinformation, and that the U.S. administration is not setting highly subjective redlines against a nuclear-capable nutterocracy, in order to sell jets.