For millennia, China has used the Korean Peninsula as a defensive barrier on its eastern flank. At the same time, the Koreas have been a constant source of security worries for its northern neighbor. Over the weekend, China's reactions to developments on either end of the peninsula reflected its complicated relationships with the two Koreas. On Sunday, in response to North Korea's continuing display of its developing nuclear weapons program, Beijing imposed a ban on imports of the country's coal through the remainder of 2017. The stinging rebuke to Pyongyang, if fully implemented, will cut the cash-strapped country's export revenue by a third. Hours later, China issued a direct warning to the South Korean conglomerate Lotte, which is nearing completion of a deal with the government in Seoul that is key to the deployment of the U.S. Terminal High-Altitude Area Defense (THAAD) antiballistic missile system.
That Beijing applied pressure against its...
