The Diplomat
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USA’s shifting policies are pushing some of its closest Asian allies to strengthen ties with one another. Japan, South Korea and Australia are building relationships that give them more options.
US Unpredictability Is Giving Its Asian Allies New Reasons to Cooperate
Author: Donggak Heo
When U.S. President Donald Trump abruptly ordered the Pentagon to substantially reduce joint military exercises with South Korea, officials in Seoul were caught off guard. The annual Ulchi Freedom Shield drills still went ahead, but were cut short on Trump’s order. The episode was a reminder that even one of Washington’s closest allies can find the assumptions of its security policy changed with little warning.
That uncertainty is why, across the Indo-Pacific, several of the United States’ closest partners are investing more heavily in relationships with one another – and, increasingly, with Europe. South Korea and Japan are expanding cooperation on supply chains, energy and advanced industries. Japan and Australia are linking economic security more closely to defense production and military operations. All three are also building more structured ties with the European Union.
Of course, these efforts are not an attempt to replace the United States. China’s growing power, North Korea’s weapons programs, Russia’s war in Ukraine, and repeated disruptions to energy and supply chains were already pushing like-minded countries closer together. But Trump’s second term has added another incentive: the need for relationships that remain useful when U.S. policy changes suddenly, including toward its own allies.
South Korea and Japan offer the most politically unlikely example. Their relationship has repeatedly been derailed by disputes over Japan’s colonial rule, wartime labor and historical memory. The rapprochement begun under former South Korean President Yoon Suk-yeol and former Japanese Prime Minister Kishida Fumio therefore looked vulnerable to political turnover.
Instead, it has continued under progressive President Lee Jae-myung and conservative Japanese Prime Minister Takaichi Sanae. In his August 15 Liberation Day address, Lee pointed to a year of shuttle diplomacy with Japan and highlighted cooperation in supply chains, energy, and advanced industries. The setting was just as important as the message: a South Korean president was emphasizing the practical value of ties with Tokyo on the day commemorating Korea’s liberation from Japanese colonial rule.
The substance has become harder to dismiss as symbolism. In March, Seoul and Tokyo signed a Supply Chain Partnership Arrangement that created mechanisms for information sharing and consultation during disruptions. Their industry ministries also established a regular policy dialogue covering trade, economic security, supply chains and mineral resources. At the Lee-Takaichi summit in May – their third in seven months – the two governments moved further into energy security, agreeing to explore emergency cooperation involving crude oil and petroleum products while strengthening supply-chain resilience.
SK Hynix is now considering a large memory-chip manufacturing investment in Japan. The project may never materialize, but its consideration is telling given the history of rivalry and trade friction between the two countries’ semiconductor sectors.
Washington once provided much of the external pressure encouraging Seoul and Tokyo to overcome their differences. Under the Biden administration, the Camp David summit in 2023 made improved bilateral ties a central part of a U.S.-led trilateral strategy. Under Trump, the logic is becoming more complicated. The United States remains indispensable to both countries, but uncertainty over U.S. trade and alliance policy is also increasing the value of a relationship that does not depend on Washington to function. The Trump administration today isn’t playing the same mediating role as its predecessor did, and yet Japan-South Korea relations are arguably closer than ever.
Japan and Australia show the same trend in a more mature form. In May, Prime Ministers Takaichi and Anthony Albanese signed a Joint Declaration on Economic Security Cooperation, committing their countries to consult during economic-security contingencies and deepen cooperation on energy, critical minerals, resilient supply chains and critical technologies.
Their defense relationship is advancing even faster. Australia is acquiring Japan’s upgraded Mogami-class frigates, while both governments are working to establish sustainment and shipbuilding capabilities in Australia. In August, they announced successful field trials of their first jointly developed defense-technology project: Boobook, a laser-based surveillance system. They are also developing arrangements for Japan to use Australian test ranges for long-range weapons, including systems linked to Japan’s hypersonic missile program. Japanese F-35s have spent weeks training in Australia, and the two militaries are expanding information sharing and operational coordination.
It would be a mistake to recast every new Australia-Japan initiative as a reaction to Trump; China is the clearest strategic driver of this partnership. Yet Tokyo and Canberra’s ability to work directly with each other is more valuable at a time when neither can assume that U.S. priorities, trade policy, or diplomatic tactics will remain consistent.
The search for additional options extends beyond Asia. South Korea and Japan both established Security and Defense Partnerships with the EU in 2024, and Australia signed its agreement with Brussels in March. Seoul and the EU are expanding cooperation on maritime security, cybersecurity, space, and defense industry policy. Japan and the EU held their second Security and Defense Dialogue in May. Australia’s new partnership with the EU spans maritime security, cyber, emerging technologies, and support for Ukraine, while Canberra and Brussels have also concluded negotiations on a free-trade agreement.
These relationships are modest compared with U.S. alliances. Europe cannot provide South Korea or Japan with extended nuclear deterrence, or replace the operational reach the United States provides Australia. But replacement is not the point. More partnerships mean more channels for coordinating supply chains, technology, energy and security when governments face a shock.
That matters because uncertainty from Washington is no longer confined to defense policy. Trump’s trade agenda has applied pressure to allies as well as competitors. In July, the administration imposed new Section 301 tariffs covering South Korea, Japan, and Australia, as well as the European Union, though applicable rates differ under existing trade arrangements. The measures reinforced a message allies had already absorbed: close security ties with Washington do not guarantee insulation from U.S. economic pressure.
For South Korea, Japan, and Australia, this makes economic resilience and strategic flexibility increasingly difficult to separate. Cooperation on critical minerals can reduce vulnerability to supply disruptions. Energy arrangements can provide alternatives during crises. Deeper technology and defense industrial ties can spread capacity across trusted partners. None of these measures protects them from every shift in U.S. policy, but they reduce the cost of having too few alternatives.
Obviously, there are limits. Seoul, Tokyo, and Canberra do not share identical threat perceptions, and historical disputes can still disrupt Japan-South Korea ties. Their relations with Europe are far less consequential militarily than their alliances with the United States. In many cases, stronger cooperation among these countries reinforces rather than competes with U.S. strategy.
But there is a difference between depending on the United States for security and depending on Washington for every form of cooperation. That distinction is becoming more important in Trump’s second term. Washington’s Asian allies are not preparing for a post-American Indo-Pacific, and there is little evidence that they want one. They are preparing for an Indo-Pacific in which the United States remains indispensable but can no longer be assumed to be predictable. The response is not to leave the United States behind, but to make sure they have more options when Washington changes course.
Credits: TCA, LLC.