South Korea's decision to pull out of the military intelligence-sharing pact with Japan endangers the close cooperation — not just between the two countries but also with their mutual ally, the United States — necessary to deal with the security threat posed by North Korea's nuclear and ballistic missile programs. Given the negative impact that a rift in trilateral cooperation could have on security in Northeast Asia, the South Korean government should rethink its decision to terminate the pact.
The General Security of Military Information Agreement (GSOMIA) was concluded between Japan and South Korea in November 2016. The pact enabled the two governments to directly share and exchange confidential information on North Korea's nuclear and missile development, which had previously been relayed only via the U.S. It was indeed a landmark agreement in the history of relations between Tokyo and Seoul, which continue to be frayed by differences over Japan's colonial rule of the Korean Peninsula and other disputes.
There are views that the termination of the GSOMIA — which would take effect in November — will have only a symbolic impact on defense intelligence sharing because both countries will continue to have access to the information by way of the U.S., with which both countries have been proceeding to integrate defense information systems. Even if it's only symbolic, however, the impact of the pact's termination will not be small as it serves as an indication of South Korea's intent to reject cooperation with Japan in general.