TOKYO — North Korea had launched its third barrage of short-range missiles in just over a week, parading its growing ability to strike its neighbors with devastating firepower.
But instead of banding together against a common adversary last week, the two American allies in the path of the missiles — Japan and South Korea — were locked in their own bitter battle with roots stretching back over 100 years.
The discord stems from Japan’s colonial occupation of the Korean Peninsula before and during World War II, and what, if anything, it still owes for abuses committed during that era, including forced labor and sexual slavery. The long-simmering conflict erupted into a full diplomatic crisis on Friday, when Japan threatened to slow down exports of materials essential to South Korean industries.
By Saturday night, thousands of protesters marched in the streets of Seoul, accusing Japan of an “economic invasion” and threatening an intelligence-sharing agreement that the United States considers crucial to monitoring North Korea’s nuclear buildup.
Washington has long relied on both countries to stand alongside it to help counter China’s rise and the nuclear-armed North. But despite the dangers of a deepening divide between its allies, the Trump administration has been reluctant to get involved to repair the rift.
President Trump said he might take some action if asked by both parties, but added that trying to referee the dispute would be “like a full-time job.” And State Department officials had said they want the two countries to work it out on their own.
Still, as tensions escalated in recent days, Secretary of State Mike Pompeo attempted on Friday to orchestrate a reconciliation at an Asian security conference attended by regional foreign ministers. A photo from the conference showed Mr. Pompeo flinging his arms wide open to the foreign ministers of the two countries, appearing to invite them to come together.
The two ministers stayed far apart, however, with Taro Kono, Japan’s foreign minister, grimacing, and South Korea’s, Kang Kyung-wha, turning away, stone-faced.
It was a telling sign not just of the worsening relationship between the two allies, but perhaps more significantly, of America’s diminished leadership role in a region where the United States has often played the part of peacemaker among its allies.
In the past, when tensions between the two nations flared, “the U.S. administration sent signals, sometimes privately, that this harms U.S. security interests,” said Michael J. Green, the senior director for Asian affairs at the National Security Council under President George W. Bush. “I think Pompeo sent that message, but it was late. It came very late from the administration.”
“Trump has made it worse,” added Mr. Green, now a professor at Georgetown. “He himself has done nothing to create a sense that there is a team of allies in Asia.”
The latest pressure point between the countries is, on the surface, a trade spat. Japan on Friday expanded controls over exports to South Korea of items ranging from ball bearings to precision machine tools.
The trade action followed an earlier move tightening controls on exports of chemicals used to make advanced semiconductors and digital flat screens — some of the most important products to the South Korean economy.
Seeming to wield trade as a political cudgel in the model of Mr. Trump, Japan cited unspecified national security concerns and suggested South Korea “mishandled” items that could be used for military purposes.
In response, President Moon Jae-in of South Korea vowed “we will never again lose to Japan,” hearkening back to Japan’s colonial occupation. Government officials said South Korea was considering withdrawing from a vital intelligence-sharing deal that the two countries, which both host American military bases, signed in 2016 at Washington’s urging.
But the current divide between South Korea and Japan is as much about their painful shared history as it is about trade.
Tensions between Japan and South Korea have waxed and waned since Japan’s surrender in World War II brought the occupation to an end.
Starting in the 1990s, relations began to warm as South Korea dropped its bans against Japanese videos and comic books. In 2002, the two countries were co-hosts of the World Cup in soccer. Tourists flow between the two countries and its companies are mutually dependent.
Still, the wounds of the colonial era have never fully healed. South Koreans argue Japan has not sufficiently apologized for its wartime atrocities while the Japanese argue they have done enough, both legally and politically.
Prospects for de-escalation seem bleak. In both countries, polls show public distrust of the other nation at their highest levels in decades.
The toll of the dispute is also starting to go beyond the economic damage of the trade standoff. Last month, two South Korean men in their 70s set themselves afire in protest against Japan. Both died.
Analysts criticized the two American allies for letting their dispute spin so far out of control.
“It’s just insane that Japan and Korea are doing this to each other,” said David C. Kang, director of the Korean Studies Institute at the University of Southern California. “They’re diverting so much energy to this. There are only so many things a government can do at one time.”
Over the decades, South Korean leaders have invoked deeply rooted nationalistic sentiments against Japan.
Prime Minister Shinzo Abe’s political party, the Liberal Democrats, has also stoked nationalist feelings in Japan with various actions, for example by proposing new language for school textbooks stating there is still a dispute about whether the Japanese Army played a direct role in forcing so-called comfort women from Korea and elsewhere to work as sex slaves for its soldiers.
In the current global climate, it may be even easier for these long-existing nationalist sentiments to intensify.
“You have an era where international leaders are much more fixated on themselves and their own political agendas and are not willing to step up and sacrifice anything for international leadership, especially here in the United States,” said Susan A. Thornton, the former acting assistant secretary of state for East Asia and the Pacific in the Trump administration and a senior fellow at Yale Law School.
“Unfortunately,” Ms. Thornton added, “it seems to be having some kind of contagion effect.”
An agreement in 2015, reached between the governments of Mr. Abe and Park Geun-hye, Mr. Moon’s impeached predecessor, was meant to settle one of the most searing disputes: how to acknowledge and compensate the Korean women who were forced to work in brothels for Japan’s military during World War II.
At the time, the two leaders called the deal a “final and irreversible resolution.”
But last November, the Moon government dissolved a foundation established under the settlement, inciting distress in Tokyo. A month earlier, South Korea’s Supreme Court ruled in the first of a series of cases awarding compensation from Japanese companies to victims conscripted as forced labor during Japan’s imperial expansion before and during World War II.
Japan argues that the court ruling violates a 1965 treaty that established diplomatic relations between the two countries and provided $500 million in aid and loans to South Korea. The treaty describes all claims arising from the colonial era as “settled completely and finally,” wording that Japan has repeatedly highlighted when arguing the Supreme Court rulings are invalid.
The two countries have tussled over various proposals to resolve the dispute, with both sides claiming the other has ignored requests for negotiations.
Now both countries seize every opportunity to taunt the other.
South Korea has canceled cultural exchanges, and consumers are boycotting Japanese beer and products from companies like Uniqlo.
In Japan over the weekend, the governor of Aichi prefecture, an independent who won a recent election with the support of Mr. Abe’s governing party, decided to shut down an art exhibition that featured a statue meant to symbolize a Korean comfort woman, citing terrorist threats if the statue was not removed.
The tiff has spilled into the military realm. Late last month, when a Russian patrol plane flew into airspace over a cluster of disputed islands that South Korea controls but Japan also claims, South Korea fired warning shots. Japan immediately said that it should have fired the shots, calling the islands “our territory.”
Such incidents can unsettle American military planners, who depend on cooperation between the allies to contain North Korea and secure the region.
“The Americans are worried that we have ships and planes in the air space and waters between these two countries,” said Daniel C. Sneider, a lecturer in East Asian studies at Stanford University. “And they have to worry about whether a Korean military vessel might fire at a Japanese military vessel.”
Trump administration officials say they are particularly concerned about the possibility that Seoul will end the intelligence-sharing agreement that Japan and South Korea reached in 2016, a key element of military cooperation that helps the United States.
That “would deal a blow to U.S. efforts to strengthen bilateral cooperation and deterrence on the Korean Peninsula,” said Bonnie S. Glaser, senior adviser for Asia at the Center for Strategic and International Studies.
Experts say the two countries will have a tough time finding a face-saving resolution without outside help. But it is not clear that either Seoul or Tokyo want help from President Trump, who dismissed the recent North Korean missile tests as “no problem,” despite the fact that such missiles would pose a direct threat to both South Korea and Japan.
A senior Trump administration official did make calls to both Japan and South Korea last week to recommend that each side freeze hostilities. South Korean officials promised to look into the proposal while Japan has denied any knowledge of it.
Mr. Pompeo had been scheduled to have one-on-one meetings on Friday with both Mr. Kono and Ms. Kang. But both meetings were canceled. Officials from all three countries said the meetings did not take place for scheduling reasons.
But another motive may have scuppered the meetings: The Japanese and South Korean foreign ministers were said to be irked by Mr. Pompeo’s pressuring them to end their differences, prompting them to take the “unprecedented” step of canceling their meetings, according to Mr. Green, the former member of the National Security Council, who cited people briefed on the events.
In Japan, where Prime Minister Abe has worked hard to cultivate a close relationship with President Trump, the government may not want to be perceived as a needy underling.
“I don’t think it’s good for the two countries that we are always asking big brother or big sister to come in and try to improve our relations,” said Ichiro Fujisaki, a former Japanese ambassador to the United States. “The Americans would probably be very angry if we tried to go in and tell them to be a little nicer to Mexico.”
Because of their historical experiences, South Koreans have always considered Japan as a rival to overcome, and they compare everything from the number of Olympic gold medals won to the number of Nobel Prize recipients.
While South Koreans take pride in overtaking Japan in industries like shipbuilding and consumer electronics, the current trade dispute provides a painful reminder that the country’s export-driven economy still depends on chemicals and other high-tech materials from Japan.
In Japan, Mr. Abe, a conservative nationalist, has also been pushing a more aggressive military posture.
Given the high passions on display, analysts said they hoped both sides would step back from the brink, with the trade fight between two economic powerhouses possibly upsetting fragile economic relationships across the globe.
“This trade dispute may on the surface look like a bilateral tit for tat,” said Wendy Cutler, a former United States trade negotiator. “But given the connected world and deep supply chains, the impact is quickly going to spill over into the region and the rest of the world.”
Eventually, the export restrictions imposed by the Japanese government could jeopardize other markets for Japanese companies. President Moon said last week that his government will lessen South Korea’s dependence on Japanese technologies and materials by finding alternative sources for imports.
“This is the typical trouble that is caused by nationalism and emotion against a potential enemy,” said Tsuneo Watanabe, a senior research fellow at the Sasakawa Peace Foundation in Tokyo. “We should be very careful to avoid unnecessary emotional conduct in state-to-state relations.”