The article explains:
South Korea installed the same system in September to protect the nation against possible missile launches from Pyongyang.
This makes sense as a temporary measure. However, it is not a long-term solution. The thing to remember in dealing with North Korea is that any perceived aggression from America will most likely result in a massive attack on South Korea by North Korea. It would be nice to avoid that. China is not really going to help in this situation–they fear being overrun with North Korean refugees. The only real pressure we can put on China is to threaten to arm Japan with nuclear weapons. That will provide a check on China’s quest for increasing power in Southeast Asia, and the threat of that might be enough to cause China to put pressure on North Korea to stop testing nuclear weapons. Meanwhile, it is being reported that the mountain North Korea has been using for its testing has collapsed.
This is a complicated mess left for the Trump Administration by the Clinton, Bush, and Obama Administrations. It may take a while to sort it all out. Hopefully, that can be done without waging war.