JEFFREY LEWIS
© AP/REX/SHUTTERSTOCK
North Korea is now, unquestionably, a nuclear power. Over the past year, under the leadership of its dictator, Kim Jong-un, it has completed a decades-long effort to acquire the ability to deliver a thermonuclear weapon against major cities in the United States. It has tested a new long-range ballistic missile, designed and produced domestically, that can strike targets thousands of miles away, as well as a thermonuclear weapon—with 10 times the destructive force of the bomb that destroyed Nagasaki—to arm it. This military build-up has been matched with tough talk from Kim.