Prime Minister Shinzo Abe of Japan, left, and President Moon Jae-in of South Korea at the G-20 summit in Osaka, Japan, in June.Credit...Pool photo by Kim Kyung-Hoon A fast-escalating trade war between South Korea and Japan took a dangerous turn this week when the Koreans abandoned a military intelligence-sharing agreement with the Japanese, weakening an important source of information on North Kor