The Wall Street Journal reports: "North Korea's nuclear test on Friday underscores the dramatically changed diplomatic landscape of North Asia, an ominous reality in what has arguably become the most dangerous corner of the planet. The degree of warmth between Ms. Park and Mr. Xi was unexpected, given that South Korea is a staunch American ally and China is North Korea's socialist bedfellow. But they had a mutual interest in cozying up. Mr. Xi sought to drive a wedge between Seoul and Washington. He also wanted to further poison Ms. Park on Japanese Prime Minister Shinzo Abe, who early in his tenure had enraged the two countries by visiting the Yasukuni war shrine, where Japanese war criminals are honored. For her part, Ms. Park invested heavily in the relationship in hopes that it would encourage Beijing to do more to restrain Pyongyang's nuclear ambitions. She's still waiting for the payoff. Judging by North Korea's latest nuclear test, its fifth, it may never come."