Today, that confrontation between Japan and South Korea moved into the national and global security realm.

It was South Korea's turn today in an increasingly serious feud with Japan.

Seoul announced the end of a key intelligence-sharing deal.

KIM YOU-GEUN, South Korean Deputy Director of National Security.

(through translator) The government has determined that maintaining the agreement, which was signed for the purpose of exchanging sensitive military intelligence on security, doesn't serve our national interests.

The general security of military information agreement fostered direct intelligence communication between Japan and South Korea, including North Korean troop movements and missile activity.

But it also helped to anchor historically rocky relations between Tokyo and Seoul.

Those took a sharp turn for the worse this summer.

Japan increased limits on exports to South Korea, including on critical tech materials used by large Korean businesses like Samsung.

YOSHIHIDE SUGA, Japanese Chief Cabinet Secretary.

(through translator): It is not our intention to have this affect Japan-South Korea relations, nor is it a countermeasure against the country.

The recent economic fight sparked mass anti-Japan demonstrations in Seoul.

But the anger rns much deeper and is centuries' old.

Daniel Russel served as an American diplomat in Japan and South Korea and oversaw the Obama administration's negotiations that resulted in the intelligence-sharing agreement.

DANIEL RUSSEL, Senior Fellow, Asia Society: Talking to South Koreans or the Japanese, they'll quickly take you back to 1592, when the Shogun Hideyoshi invaded South Korea.

There is a long litany of grievances.

Particularly in the last three years, there has been steady series of events.

One slap is met by another slap between Seoul and Tokyo.

At the root, profound Korean national resentment of imperial Japan's sexual enslavement of Korean women during World War II.

In 2015, Japan met longstanding Korean demands for an official apology for the abuse of so-called comfort women in an agreement with Korea's former President Park Geun-Hye.

But President Moon Jae-in revoked that agreement when he came to power in 2016.

MOON JAE-IN, South Korean President (through translator): On the issue of comfort women, wartime crimes against humanity can't be swept under the rug by saying it's over.

Aging survivors still shaken by the trauma, continue to demand more from Japanese President Shinzo Abe.

KIM JEONG-JU, Former Forced Laborer.

(through translator): In Japan, I was so hungry that I had to eat grass from our dorm garden and my hair fell off.

I lived like a slave there, but Abe is saying like it was not.

Korea's younger generation demonstrated their outrage, too.

NOH MIN OCK, South Korean Student (through translator): They're still not owning up to the past, and instead of apologizing to the victims of forced labor, they are engaging in economic retaliation.

It makes me really angry.

All of this weakens a critical alliance for Washington, and military officials are concerned.

Marine Corps Commandant David Berger: GEN.

DAVID BERGER, U.S. Marine Corps Commandant: But, from a military perspective, it's important to be able to share information, because each country has information that the other ones will need.

U.S. Secretary of State Mike Pompeo had this to say today

MIKE POMPEO, U.S. Secretary of State: We're disappointed to see the decision that the South Koreans made about that information-sharing agreement.

And we hope each of those two countries can begin to put that relationship back in exactly the right place.

But the uptick in tension could be a symptom of White House policies at a critical moment for the Korean Peninsula.

There have been series of actions and reactions that should have caused the Trump administration not to mediate, but to moderate, to remind both allies that we face a common danger from North Korea.

The risk to American citizens is vastly increased when there is a degradation in the networked security alliance, faced with a threat like North Korea.