The long-awaited summit between President Trump and Chairman Kim will be about more than just U.S.-North Korea relations. An ideal outcome would be a deal regarding nuclear disarmaments offset against relaxed trade sanctions. The latter appear to have been what has driven North Korea to the negotiating table. The DPRK’s global trade may fall to as little as $2.4 billion in 2018 from a peak of $8 billion in 2013. That’s been down in large part to a sanctions-driven slump in Chinese imports from North Korea to just $81 million in the first four months of 2018. A return to 2016 trade levels...