There have been many ups and downs before this military intelligence sharing deal was finally signed. South Korea and Japan were on the verge of signing off on the pact in June 2012, but Seoul backtracked at the last minute in response to public outcry.

Before the pact came into force, South Korea and Japan needed to go through Washington when sharing defense intelligence under a deal inked in 2014. This new deal remains highly controversial in South Korea, where the legacy of Japan's harsh colonial rule of the Korean Peninsula from 1910 to 1945 still triggers negative sentiment and many South Koreans believe Tokyo has never properly atoned for the abuses of the time.