But the decision to leave the agreement is a major blow to the United States-led military alliance, which for decades has been helping to bring peace to Northeast Asia, while resisting increasing Chinese influence.
China and North Korea have long sought to reduce US military presence in Northeast Asia by throwing wrenches at the trilateral relations between Washington, Seoul and Tokyo.
The weakest link in this triangle is between Seoul and Tokyo, who deeply trust each other because of the legacy of the colonization of Korea in Japan. Critics of the Trump administration's policy in Northeast Asia have accused the president of neglecting Washington's traditional role in mediating between South Korea and Japan.
"The United States is a common point between the two bilateral alliances and is far less effective in moving information in both directions," said retired general Vincent Brooks, who commanded the United States and South Korea.
Practically speaking, abandoning the intelligence sharing agreement will delay things.
The agreement allowed the two countries to "share seamless military intelligence," but as it stands, the United States will be forced to play the role of middle man, said Abraham Denmark, a former deputy assistant, US Secretary of Defense so for East Asia.
"This slows down decision-making, which is frustrating every day but could have serious consequences in the face of a rapidly developing crisis."
It is also likely to ease China, an ambitious regional power that claims that the islands are administered by Japan and repelled by South Korea over the deployment of US missile defense.
The recent advances in Chinese military concerns have raised US defense chiefs, who earlier reported that Beijing intended to become "a dominant force in the Indo-Pacific."
Since 2014, China has released more submarines, warships, major ships and auxiliary amphibians out of the total number of ships currently serving the naval forces in Germany, India, Spain, Taiwan and the United Kingdom, according to a 2018 Brain Report the IISS trust.
The Chinese Air Force also regularly makes new and sophisticated aircraft and weapons, including the twin-engine J-20 stealth.
To counter this ambition, The US needs to step up cooperation with Asian defense partners. In a statement on Friday, Japan's Defense Minister Takeshi Iveya said South Korea's move shows a "misunderstanding" of the current security situation in the region.
"It is extremely regrettable and disappointing," Ivaya said.
United States Secretary of State Mike Pompeo said he was "disappointed" by Seoul's decision to leave the agreement, adding that he hoped "these two countries would start to bring that connection back to the right place."
What this means  Although the only two liberal democracies in the region, Seoul and Tokyo are essentially friends of convenience thanks to each country's treaty alliance with the United States. They are historical adversaries, and the legacy of Japan's colonization on the Korean Peninsula in Japan in the first half of the 20th century is emerging. Under Japanese rule, many Koreans were brutalized, killed and enslaved. It is still a living memory for the elderly Koreans and remains a highly emotional topic in both North and South Korea.
South Korea and Japan signed a treaty in 1965 that normalized relations between the two countries and had to settle long-term military issues.  But South Korea was a military dictatorship at the time, and many Koreans thought the deal was unfair.
Japan claims that the two issues are settled by the treaty.
But despite the historical hostility, military relations between the two countries have been largely affected. Washington's traditional job was to straighten both sides of the table, overcome the problems, and sell them the benefits of unity in the face of threats from Pyongyang or Beijing.
President Donald Trump, however, seems to deviate from this role. He has publicly questioned the value of investing so much US money into alliance networks in the region, and urged both South Korea and Japan to invest more in their military partnership with the United States.
The military spy has been dating before because the Trump administration has not invested enough time or shown that it is interested in maintaining the union as much as its predecessors, said Van Jackson, a former Department of Defense official with the Obama specializing in Northeast Asia.
"This could have happened at any time in the last 20 years and the only reason it was not was because of middle-class people and political appointees in the US who spent significant amounts of time and political capital.
"This is a boon for those who would like US power in Asia to shrink and its alliances to weaken – especially China and North Korea," said Denmark, now director of the Asia program at the Woodrow Wilson International Center  "Both see the United States as their main enemy and the United States as a major obstacle to their strategic goals. The problems between the US alliances – especially those as critical as Japan and South Korea – are seen as a challenge to the US strategist th, but also a symbol of reducing American power in Asia. "