South Korea recently announced it would restart negotiations with Japan for a military and intelligence sharing agreement. Washington should encourage this growing security cooperation.

Moon Sang-gyun, spokesman for South Korea’s Ministry of National Defense, said Sept. 27 that North Korea’s “nuclear and missile threats are escalating by the day, so our security situation is becoming more critical.”

My own recent private discussions with government officials in Seoul confirmed South Korea’s intent to move forward on the agreement, formally called a General Security of Military Information Agreement (GSOMIA).

The GSOMIA would be the first military pact between Seoul and Tokyo since 1945. Though historic, the agreement is simply a legal framework of required methods to protect classified information that allows for the bilateral exchange of intelligence about North Korea’s nuclear, missile, submarine, and conventional force threats as well as potential military and cyberattacks.

History Impeded Progress

While Washington has strong alliances with both South Korea and Japan, the security relations between Seoul and Tokyo have been extremely limited due to territorial disputes and bitter historical animosities dating to Japan’s brutal, 35-year occupation of the Korean Peninsula between 1910 and 1945.

In June 2012, South Korea and Japan were within an hour of signing a General Security of Military Information Agreement, but Seoul canceled at the last moment. The reasons: fierce domestic criticism and legislative backlash over the secretive nature of the talks and the prospect of signing a pact with Korea’s former colonial oppressor.

The head of the opposition party at the time accused the South Korean government of seeking “to give access without restriction to military facilities and intelligence in seeking to forge a military intelligence treaty with a country that invaded our nation in the past.”

In reality, under the planned agreement Seoul and Tokyo would retain authority for deciding what data are shared.

Despite the collapse of the agreement, Seoul and Tokyo continued to quietly improve bilateral security relations. They exchanged observers during military exercises and engaged in trilateral naval and missile defense training exercises with the United States.

The U.S., South Korea, and Japan signed a limited intelligence sharing agreement in December 2014, but it still required Washington to be the intermediary for information provided by Seoul and Tokyo. While that agreement was an improvement, it still didn’t enable effective, real-time security cooperation during a crisis or attack.

Recent progress was enabled by the December 2015 bilateral agreement on South Korean women forced into sexual slavery—they were known euphemistically as “comfort women”—during the 1910-1945 Japanese occupation.

The landmark agreement was a stunning success achieved through diplomatic perseverance, as well as political courage by Japanese Prime Minister Shinzo Abe and South Korean President Park Geun-hye to push back against nationalist elements in their respective countries.

This past March, the U.S., Japanese, and South Korean leaders pledged to increase military cooperation against the growing North Korean threats.

On Oct. 14, South Korean Defense Minister Han Min-koo explained that “the need has heightened” for the bilateral agreement because of North Korea’s two nuclear tests and breakthrough successes on several missile systems in 2016.

Seoul is also probably more receptive given China’s heavy-handed threats of economic, diplomatic, and military pressure against the U.S. in deploying the missile defense system known as Terminal High Altitude Area Defense, or THAAD,  in South Korea.

Critical for Allied Security

A bilateral General Security of Military Information Agreement between America’s critical northeast Asian allies would improve deterrence and defense capabilities against Pyongyang’s escalating nuclear and missile threats. Currently, for example, U.S. military officers must turn off live feeds from South Korean or Japanese sensors when representatives of the other ally enter a command or intelligence center.

Removing the intelligence-sharing constraints would be in South Korea’s national interests, since it would enable access to North Korean threat data from Japan’s high-tech intelligence satellites, AEGIS ships, and early warning and anti-submarine aircraft. South Korea could provide information on the North’s missiles detected by long-range air search radar.

Both South Korea and Japan have extensive, highly capable militaries. Given Pyongyang’s large submarine fleet and successful launch of a submarine-launched ballistic missile this year, coordinated trilateral anti-submarine and counter-mining operations are increasingly important.

The GSOMIA also is necessary for a comprehensive allied missile defense system in Asia. Integrating South Korea, Japanese, and U.S. warning sensors and tracking radars would enhance real-time missile defense security for all three countries. However, to date, South Korea has refused to integrate its Korea Air and Missile Defense system into the more comprehensive and effective allied ballistic missile defense system.

Despite the clear and present danger from North Korean missiles, South Korea insists on maintaining an independent and less capable missile defense system to protect its citizens and U.S. forces in Korea against the North’s nuclear, biological, and chemical missile attacks.

In addition to signing the agreement, South Korea should integrate its missile defense system into the comprehensive allied system with linked sensors to improve deterrence and defense capabilities for the forces of all three countries.

What Washington Should Do

U.S. interests in Asia—ensuring regional stability, protecting maritime freedom of navigation, and peaceful resolution of disputes—benefit from greater multilateral cooperation.

Washington therefore should continue policies to augment bilateral and trilateral military cooperation efforts with Seoul and Tokyo, particularly in missile defense against the North Korean threat.

Strong trilateral security cooperation also can affirm recently improving South Korea-Japanese relations and form the basis for addressing other regional and global security challenges.

The U.S. will remain the guarantor of regional stability and should:

• Publicly highlight the need for greater South Korean-Japanese military and diplomatic cooperation as a vial component of comprehensive security efforts against North Korea’s growing military threat. While the immediate need is on missile defense and anti-submarine operations, Japan and South Korea should discuss potential joint peacekeeping missions, counterterrorism, counterpiracy, and disaster response operations.

• Step up trilateral military exercises to increase transparency, augment familiarity of operations necessary during a crisis, and improve combined capabilities.

• Continue to affirm unequivocal military support for South Korea and Japan, including the U.S. extended deterrence guarantee of the nuclear umbrella, missile defense, and conventional forces.

• Maintain robust, forward-deployed military forces in South Korea, Japan, and the Western Pacific to deter, defend, and defeat security threats to U.S. national interests and American allies. The U.S. presence also should allay South Korean concerns over Japan’s defense reforms and slowly growing security role.

• Privately counsel both South Korea and Japan to make progress on implementing the December 2015 “comfort women” agreement and refrain from comments and actions that could incite nationalist responses in either country.

• Propose an annual trilateral meeting of the three countries’ foreign and defense ministers (a “2+2+2 meeting”) to develop a joint strategic vision and integrate roles, missions, and capabilities.

A Necessity

U.S. national interests and ability to defend them are enhanced by greater cooperation among our allies. This is particularly true between South Korea and Japan, which recently have overcome strained bilateral relations.

The growing military capabilities of North Korea and China, and their willingness to use them to test international resolve, have increased tensions and the risk of military incidents or clashes.

While the actions by Pyongyang and Beijing are inimical to allied interests, they have crystalized the necessity that South Korea and Japan overcome historic differences to address current and future threats.

Washington should welcome and encourage growing South Korean-Japanese security cooperation.