The first step should begin immediately, well in advance and without firing a shot. All military family members, all Department of Defense civilian employees and all nonessential contractors should be evacuated from South Korea. Want to get North Korea’s attention? That single act would serve as a graver warning of our readiness than any amount of sanctions or saber-rattling. Initially, we’d launch a surprise air and naval campaign, with ground forces deployed only in defense of South Korea. Pyongyang’s nuclear and missile-development facilities and arsenals wouldn’t be in the initial target set. First, we’d have to overwhelm and destroy North...