Kim’s nuclear test site collapsed, killing many of his scientists and destroying his nuclear program. Some radiation leaked out and crossed into China. Kim was summoned to Beijing and was told enough is enough, if you want to stay alive stop the rhetoric, stop the testing, make peace. If you do we will support you, let you remain in power, and let your country make lots of money by following our example. If you don’t we will get rid of you.
That’s all just speculation, of course.
China’s the man behind the curtain.