（從左至右）澳大利亞副總理理乍得·馬爾斯、日本外務大臣岩屋毅、北約秘書長馬克·呂特、新西蘭總理克里斯托弗·拉克森、韓國國家安全顧問魏聖洛在2025年6月25日舉行的海牙北約峰會上

二戰後，美國在亞太廣大地區保持着幾無爭議的主導地位。在“舊金山體系”或“軸輻”架構下，美國建立了軍事同盟，提供經濟援助，並積極介入該地區事務。美國政策的戰略基礎有賴雙邊和多邊防務協議，如與日本（1951年）、韓國（1953年）、菲律賓（1951年）、澳大利亞和新西蘭（統稱ANZUS，1951年）以及泰國（1954年）的協議。

美國向該地區提供經濟援助，並在重建中發揮了作用。它通過“道奇計劃”支持日本穩定經濟，並在朝鮮戰爭（1950-1953年）後向韓國提供援助。美國主導的IMF和世界銀行也向各國提供了援助。同時，華盛頓向歐洲盟友施壓，要求它們放棄在亞洲的殖民地。美國的經濟和技術援助推動了1960-1990年代“亞洲四小龍”（韓國、香港、新加坡和台灣）的崛起。

美國目前正扭轉這些政策。這一逆轉趨勢早就出現，但唐納德·特朗普總統2025年1月開始的第二任期內的政策加速了這一進程。他的“美國優先”政策正在重塑美國與亞太國家在國防、聯盟模式和經濟領域的關係。

特朗普將美國對亞太盟友的承諾與“更高的成本、更多的要求和不一致的條件”掛鉤。他敦促盟國將國防預算提高到GDP的5%，並在共同安全領域承擔最大份額。針對印度購買俄羅斯武器和石油，特朗普加征關稅，這是近年來兩國關係首次遭受重大打擊。他的政策引發該地區許多國家民眾的不滿和外交緊張局勢。例如，日本取消了原定於7月1日與美國舉行的“2+2”會談；澳大利亞總理安東尼·阿爾巴尼斯公開拒絕美國大幅增加國防開支的呼籲；日、澳、韓高層領導人缺席海牙北約峰會，只派出級別較低的官員；韓國國防部正式拒絕了增加國防預算的要求。

除了導致雙邊關係緊張，特朗普的政策還影響到至少兩個美國主導的小多邊安全框架：日美印澳四方安全對話（Quad）和澳英美安全夥伴關係（AUKUS）。2007年成立的Quad旨在協調印太地區的人道主義援助和救災行動，加強海上安全。2017年重啟後的Quad則是為了深化在海上安全、關鍵基礎設施、互聯互通、供應鏈韌性和新興技術方面的戰略合作，以推動“自由、開放和基於規則的印太地區”，暗中反對中國的政策。然而，由於美國疏遠了與其他成員的關係，該機制未來的有效性目前尚不確定。

同樣，AUKUS也面臨不確定的未來。AUKUS於2021年啟動，旨在為澳大利亞配備先進的核動力潛艇，並在網絡、人工智能、量子技術和海底作戰等前沿領域建立三邊合作框架，其戰略意圖是對抗中國在印太地區日益增長的軍事影響力。

五角大樓正在審查與澳大利亞和英國共享核動力潛艇技術的AUKUS協議。

2024年3月10日，洛杉磯級快速攻擊潛艇“安納波利斯”號停靠在西澳大利亞羅金厄姆西艦隊基地的迪亞曼蒂納碼頭。（MC2 Kaitlyn Eads / 美國海軍）。

2025年6月，美國國防部啟動對價值3680億澳元（約2400億美元）的AUKUS協議的正式審查，評估其是否符合特朗普政府的“美國優先”議程和美國國防工業利益。該審查由負責政策的國防部副部長埃爾布里奇·科爾比牽頭，預計將在未來幾個月內完成。英國和澳大利亞都公開強調對AUKUS的承諾，但也承認在美國政策不確定情況下對該項目的未來感到擔憂。美國與日本、澳大利亞和印度等主要戰略盟友的關係脫節，引發了人們對Quad和AUKUS未來前景的憂慮。

在經濟領域，與二戰後美國的經濟援助和市場開放政策不同，特朗普政府實行了保護主義。從4月2日即所謂“解放日”開始，他加征了一系列高額關稅。儘管美國已經與一些國家簽下貿易協定，並正與其他國家進行談判，但所有亞太國家都深受這些關稅的影響。即使在最終達成的貿易協定里，美國的關稅也明顯高於4月2日之前的水平，例如相較“解放日”之前，美國對日本的關稅達到15%，對韓國關稅為15%，對越南關稅為20%。

加征關稅前，特朗普政府大幅還削減了美國的全球對外援助，包括削減美國國際開發署資金、全球衛生項目、給世界糧食計劃署的捐款、氣變項目及公共廣播。2025年6月，特朗普政府向國會提交了一份報告，提議削減關鍵領域83億美元的對外援助。雖然特朗普政府的這種做法有其自身理由，但關稅和援助削減嚴重影響了特別脆弱的經濟體和小國。例如，太平洋小島國首當其衝地受到了援助削減和高額關稅的雙重打擊。

特朗普政府迅速、單方面地實施這些重大變革，並未與地區國家進行協商，導致許多國家陷入恐慌。大多數國家選擇不回應，擔心受到美國的進一步報復，但它們的不滿情緒顯而易見。

亞太地區的二戰後安全框架在結構上已經過時，與該地區的快速變化格格不入，特朗普政府的政策更加速了它的瓦解和分裂。日本、韓國、澳大利亞和印度等盟友對美國政策表達了擔憂，Quad和AUKUS的命運正標誌着這種瓦解。許多地區國家認為，如果它們必須承擔自身國防費用並支付高額關稅才能進入美國市場，那麼採取符合本國議程的政策要比遵從美國的路線更好。

不斷演變的模式表明，由於美國承諾的不確定性，該地區主要國家將增加國防預算，同時重新評估與其他國家尤其同中國的關係，雖然過去它們尋求美國的支持與之抗衡。如今，與中國進行不受美國安全承諾影響的接觸將為它們提供新的思考角度。其實，這種趨勢始於特朗普第二任期之前，2024年日本、韓國、澳大利亞和印度等國的對華關係已經升溫。

此外，這些國家中等強國地位的日益增強，也促使它們建立自身能動性和民族主義觀，而不是被當作美國亞太戰略的次要參與者。例如，日本有自己的願景，並希望利用它來塑造地區政治。同樣，印度長期以來一直保持戰略自主，並偏愛小多邊主義。一旦亞太地區由外部強加的安全秩序減弱，就可能導致地緣經濟取代地緣政治，小多邊主義和多極化取代單邊主義。

許多分析人士認為，特朗普應對美國在亞太地區影響力的變化（下降）負責。但深入分析表明，特朗普只是結果，而非原因。美國是“大國興衰”這一人類歷史常見主題的典型案例。美國全球霸權的過度擴張、盲目支持以色列在加沙被佔地帶實行種族滅絕的道德破產、不斷攀升的債務以及日益惡化的經濟問題，都意味着美國政策應有結構性轉變。特朗普正試圖用自己的方式解決美國這些積弊。美國在亞太地區數十年的影響力正在發生變化，誰將填補這一空白，該地區未來的安全格局將如何演變，仍有待觀察。

From left: Richard Marles (Deputy Prime Minister, Australia), Takeshi Iwaya (Minister of Foreign Affairs, Japan), NATO Secretary General Mark Rutte, Christopher Luxon (Prime Minister, New Zealand), Wi Sung Lac (National Security Advisor, Republic of Korea) meet at the NATO summit in The Hague, Netherlands, June 25, 2025. (Photo: NATO)

In the post-World War II period, the U.S. maintained nearly uncontested supremacy over the vast Asia-Pacific region. Under the San Francisco System, or the 'Hub and Spokes' architecture, the U.S. established military alliances, provided economic assistance, and proactively engaged with the region. The strategic foundation of U.S. policy relied on both bilateral and multilateral defense agreements, such as those with Japan (1951), South Korea (1953), the Philippines (1951), Australia, New Zealand (collectively known as ANZUS, 1951), and Thailand (1954).

The U.S. provided economic assistance and played a role in the region's reconstruction. It supported Japan through the Dodge Plan to stabilize its economy and, following the Korean War (1950-1953), offered aid to Seoul. The U.S.-led IMF and the World Bank also assisted various countries. Washington pressured its European allies to relinquish their colonies in Asia. U.S. economic and technological assistance contributed to the rise of the Asian Tigers, South Korea, Hong Kong, Singapore, and Taiwan, from the 1960s to the 1990s.

The U.S. is now reversing these policies. While this reversal trend had started earlier, the policies of President Donald Trump during his second term, beginning in January 2025, accelerated it. His 'America First' policy is reshaping U.S. relations with Asia-Pacific countries in defense, alliance patterns, and economic domains.

Trump is linking the U.S. commitment to Asia-Pacific allies with 'higher costs, more demands, and inconsistent conditions.' He pushed allies to increase their defense budgets to 5 percent of GDP and bear the lion's share in common security. Trump imposed heavier tariffs on India for purchasing Russian arms and oil, marking the first significant blow to U.S.-India relations in recent times. His policies sparked public dissatisfaction and diplomatic tensions in many countries of the region. For instance, Japan cancelled its planned 2+2 meeting with the U.S. set for July 1; Australia's Prime Minister Anthony Albanese publicly rejected U.S. calls for a significant boost in defense spending; top leaders of Japan, Australia, and South Korea skipped the NATO summit in The Hague and instead sent lower ranking officials; South Korea's defense ministry formally rejected the demand for an increase in defense budget.

Besides straining bilateral relations, Trump's policies have affected at least two U.S.-led minilateral security frameworks: the Quad (Quadrilateral Security Dialogue), which includes Japan, the U.S., India, and Australia, and AUKUS (Australia-United Kingdom-United States). The Quad was established in 2007 to coordinate humanitarian assistance, disaster relief, and strengthen maritime security in the Indo-Pacific region. After its revival in 2017, the Quad aimed to deepen strategic cooperation on maritime security, critical infrastructure, connectivity, supply-chain resilience, and emerging technology to promote a 'free, open, and rules-based Indo-Pacific,' implicitly opposing China's policies. However, by alienating all other members, the future effectiveness of the mechanism is now uncertain.

Similarly, AUKUS faces an uncertain future. Launched in 2021, AUKUS was designed to equip Australia with advanced nuclear-powered submarines and to establish a trilateral framework for collaboration in cutting-edge areas such as cyber, artificial intelligence, quantum technologies, and undersea warfare, with the strategic intent to counter China's growing military influence in the Indo-Pacific region.

The Pentagon is reviewing the AUKUS agreement on sharing nuclear-powered submarine technology with Australia and the United Kingdom.

The Los Angeles-class fast-attack submarine Annapolis pulls alongside Diamantina Pier at Fleet Base West in Rockingham, Western Australia, on March 10, 2024. (MC2 Kaitlyn Eads / U.S. Navy)

In June 2025, the U.S. Department of Defense initiated a formal review of the A$368 billion (approximately US$240 billion) AUKUS deal, assessing whether it aligns with the Trump administration's 'America First' agenda and U.S. defense industrial interests. The review, led by Under Secretary of Defense for Policy Elbridge Colby, is expected to be completed in the next few months. Both the UK and Australia have publicly emphasized their commitment to AUKUS but acknowledge concerns about the project's future amid U.S. policy uncertainty. The disconnect in U.S. relations with key strategic allies Japan, Australia, and India raises doubts about the future of both the Quad and AUKUS.

In the economic sector, unlike the post-WWII U.S. policy of economic assistance and opening markets, the Trump administration adopted protectionism and imposed a series of steep tariffs starting from April 2, the so-called 'Liberation Day.' Although the U.S. has signed trade deals with some countries and is negotiating with others, all Asia-Pacific countries have been deeply affected by these tariffs. Even in the final trade agreements, U.S. tariffs are significantly higher than those that existed before April 2. For instance, the tariffs with Japan are set at 15%, with South Korea at 15%, and with Vietnam at 20%, compared to what existed before 'Liberation Day.'

Prior to the tariffs, the Trump administration significantly reduced U.S. global foreign aid, including cuts to USAID funding, global health programs, contributions to the World Food Program, climate change, and public broadcasting. In June 2025, the Trump administration submitted a report to Congress that proposed cutting US$8.3 billion in foreign aid in key areas. While the Trump administration's approach has its own rationale, these tariffs and aid cuts have severely impacted especially vulnerable economies and small countries. For instance, small Pacific Island Countries faced the brunt of simultaneous aid reductions and heavy tariffs.

The Trump administration implemented these significant changes quickly, unilaterally and without consulting regional countries. This caused a state of panic for many nations. Although most countries chose not to respond, fearing further retaliation, their discontent was evident.

The post-WWII security architecture in the Asia-Pacific had become structurally obsolete, mismatched with the rapid changes in the region; policies of the Trump administration accelerated its erosion and fragmentation. Expressing concerns against U.S. policies by allies such as Japan, South Korea, Australia, and India, the fate of the Quad and AUKUS signals this erosion. Many regional countries believe that if they have to bear the burden of their own defense and pay steep tariffs to access the U.S. market, it would be better to adopt policies that align with their own national agendas rather than toeing the U.S. line.

The evolving pattern indicates that major regional countries will increase their defense budgets due to uncertainties surrounding U.S. commitments. At the same time, they will reassess their relations with others, particularly with China, against whom they had sought U.S. backing. Engaging with China independently of U.S. security commitments would provide them with a new perspective. This trend had already begun even before Trump's second term. Japan, South Korea, Australia, and India, among others, had started to warm up to China by 2024.

Furthermore, the growing middle power status of these countries compels them to develop their own agency and nationalistic outlook rather than being seen as secondary players in the U.S. Asia-Pacific strategy. For example, Japan has its own vision that it aims to use to shape regional politics. Similarly, India has long maintained strategic autonomy and a preference for minilateralism. Once an externally imposed security order in the Asia-Pacific weakens, it could lead to geoeconomics superseding geopolitics, and minilateralism and multipolarity superseding unilateralism.

Many analysts hold Trump responsible for the shifts (read decline) in U.S. influence in the Asia-Pacific. A deeper examination shows that Trump is an effect, not the cause. The U.S. represents a typical case of the 'rise and fall of great powers,' a common theme in human history. The overstretched global hegemony of the U.S., exposure of its moral bankruptcy as seen through its blind support for Israeli genocide in occupied Gaza, the mounting debt, and compounding economic challenges necessitated structural changes in U.S. policies. Trump is trying to address these accumulated American problems in his own way. The decades-old U.S. influence in the Asia-Pacific is changing. Who will fill the void and what the future security structure of the region will be, remains to be seen.