South Korea should engage more proactively with Japan and through their common ally, the US, as Japan’s pursuit of its largest military buildup since its post-World War II pacifism days heralds a new phase of military competition, according to experts.

The outreach would help prevent the kind of arms buildup reminiscent of Japan’s wartime aggression, they said Tuesday.

Tokyo’s five-year $322 billion defense strategy, unveiled two weeks ago, is twice the amount spent in the last five years. Seoul feels ever more on edge, however, because the plan condones deploying missiles that can hit foreign targets for the first time if an attack appears “imminent” -- a reversal of Japan’s purely defensive strategy and an attempt at a broader interpretation of its war-renouncing constitution.

Whether the latest change is against the constitution or not is still debated, even in Japan.

“What’s clear though is that we can communicate to them our concerns about the major shift the Japanese are making. We have a declaration discussing Japan’s commitment to pacifism and nonproliferation, and the two leaders (of South Korea and Japan) already shook hands on it. So I’d say that could be a start,” said Nam Ki-jeong, acting director at Seoul National University’s Institute for Japanese Studies.

The 1998 declaration -- then signed by President Kim Dae-jung and Japanese Prime Minister Keizo Obuchi -- set the terms for a new Korea-Japan partnership and has since worked as foundation for ties, even as the two neighbors were locked in longtime historical disputes, according to Nam.

It has become more important than ever as Japan increasingly and more brazenly seeks to look the other way, Nam added, noting the timing is favorable for the Yoon Suk-yeol administration to bring up the matter.

President Yoon, who took office in May, vowed to use the declaration to mend ties at a ceremony held on Aug. 15 to mark the end of Japan’s 1910-45 colonial rule of the Korean Peninsula.

Containing an emboldened Japan should also involve using the three-way military coalition that includes the US to prevent an unwanted conflict from breaking out on the peninsula, said Lee Won-deog, a professor of Japanese studies at Kookmin University.

“It’s clear that the US backs a stronger Japan, so we have to be smart about how we make sure a war is not accidentally set off here,” Lee said, referring to the recent debate over dealing with a potential counterstrike on North Korea by Japan.

South Korea sees the North as part of its territory, despite the fact that they are recognized separately on the international stage. Theoretically, an attack on Pyongyang could translate to a breach of Seoul’s territorial integrity -- reasoning that makes the fallout from Japan’s unwarranted attack on North Korea ever more complicated.

So far, the Yoon administration has refused to even entertain such a scenario, saying anything involving the Korean Peninsula requires Seoul’s say-so in advance. Tokyo disputes this, citing self-defense.

The discord is evidence that the two countries have yet to fine-tune details regarding the rules when it comes to engaging North Korea, Lee said, urging Seoul to sit down with Washington and Tokyo to address the issue. Opening dialogue, Lee stressed, should not invite as much hesitation or even resistance from the US as enlisting Washington’s help in dialing down Japan’s military buildup altogether.

“Japan first has to talk with the US, its biggest ally, before any military action. The US in turn would then have to reach out to South Korea, another Asian ally. So the three need a protocol anyway to straighten out any potential problems arising from that kind of discourse,” Lee said.

Choi Eun-mi, a research fellow at the Asan Institute for Policy Studies, said South Korea should be able to take a clearer stand on North Korea, referring to the fact that Seoul sees Pyongyang as a military threat to rein in while at the same time considering it a neighbor with whom to do economic exchanges.

“Pyongyang is just a threat to both Washington and Tokyo. But Seoul doesn’t see it the same way 100 percent, which makes discussing a more united front on North Korea all the trickier in case of more flagrant aggression,” Choi said.