SEOUL — A sense of impending crisis is deepening in Northeast Asia 78 years after the Japanese surrender ended the bloodiest war in the region’s history.

This time, in a role reversal to friendship from enmity, Japan and South Korea, though still simmering with grievances, share common cause against the danger of a new conflagration far worse than the war that ravaged the region between the attack on Pearl Harbor in 1941 and the Japanese surrender on August 15, 1945, after the atomic bombing of Hiroshima and Nagasaki.

It’s with memories of World War II, “the Pacific War” to Japanese, that the American, Japanese, and Korean leaders will be meeting Friday at the congenial surroundings of Camp David, northwest of Washington, D.C., for a strategy session that should be much more than a love-in among friends.

The confab will undoubtedly wind up with a statement of unity and total cooperation against North Korea and the North’s prime benefactor, Communist China, but there should be much more to the occasion than backslapping and happy talk. In one day they should lay out mutual strategic aims that would have appeared impossible just a few years ago.

President Yoon, anxious to head off domestic criticism of his pro-Japan policy, observed the holiday marking “liberation” by proclaiming South Korea and Japan as “partners who share universal values and pursue common interests.” Together, he said, they can “cooperate on security and the economy” and “contribute to peace and prosperity across the globe.”

That’s a message that millions of Koreans have difficulty accepting while at odds with Japan on issues ranging from payment for Koreans forced to work in Japanese factories in World War II to compensation for “comfort women” who served Japanese soldiers. Other festering issues cover the cruelties of Japanese colonial rule of Korea, between 1910 and the Japanese surrender.

Against all these memories, though, Mr. Biden appears confident he can draw Mr. Yoon and Prime Minister Kishida together in a show of “trilateral” interests. The relationship comes close to alliance, which all sides recognize is impossible considering the long history of hostility between Japan and Korea.

Increasingly strident rhetoric from North Korea’s leader, Kim Jong-un, has made it all the easier for Korea and Japan to work as de facto allies. Mr. Kim in recent days has done his best, it seems, to convince South Korean and Japanese leaders of the need to forget the constraints of the past and join forces against a foe that could easily rain down missiles on military targets in both countries.

Most recently, Pyongyang’s Korean Central News Agency has reported Mr. Kim as setting “an important goal to drastically boost the existing missile production capacity.” The newspaper of the North’s ruling Workers Party, Rodong Sinmun, ran a photograph showing Mr. Kim at the wheel of a “newly developed utility combat armored vehicle” during a tour of a munitions factory.

Mr. Yoon in his remarks took a swipe at his critics, both at home and abroad, particularly among leftist activists in America, who have opposed the direction he’s taken Korean foreign policy since his election to a five-year term in March of last year. “We must never succumb to the forces of communist totalitarianism,” he vowed. “We must not be deceived by those who follow and serve them.”

A sure sign of the shift in policy under Mr. Yoon is that Korean and American forces have resumed live-ammunition war games. Next Monday, they’re opening 10 days of exercises featuring air, ground, and naval forces — training his liberal predecessor, Moon Jae-in, had barred. Mr. Moon, having met Kim Jong-un in three summits in 2018, dreamed of reconciliation on the Korean peninsula, but was rebuffed by the North.

China saw the show of trilateral cooperation as a bid by Washington “to create a ‘mini NATO,” a regional alliance similar to the North Atlantic Treaty Organization binding America and 30 other countries. The English-language organ of the ruling Chinese Communist Party, Global Times, warned that such a grouping “would pose a huge threat to regional peace and stability.”

The Chinese, meanwhile, were playing games of their own. China’s defense minister, Li Shangfu, has left for “the Moscow Conference on International Security” and then a visit to Belarus, Moscow’s close ally, winding up on Saturday, the day after Messrs. Biden, Kishida, and Yoon are to meet at Camp David.