From Foes to Friends

Once yesterday’s enemy, Japan is fast becoming America’s strongest military partner in the Pacific to counter China’s growing assertiveness.

Few transformations in geopolitics are as striking as Japan’s evolution from a bitter wartime adversary of the United States into one of its most critical military allies. In the shadow of China’s expanding military presence, this alliance has entered a new phase, marked by deeper military cooperation and strategic realignments. With U.S. Defence Secretary Pete Hegseth’s recent visit to Tokyo underscoring the urgency of deterrence, Japan is shedding its post-war pacifism and embracing a more assertive defence posture.

For much of the late 19th and early 20th centuries, Japan’s military expansionism placed it at odds with both the U.S. and China. The Sino-Japanese War (1894-95) saw Japan dismantle Qing China’s hold over Korea and seize Taiwan, laying the groundwork for its imperial ambitions. The early 20th century witnessed Japan’s growing regional dominance, culminating in its invasion of Manchuria in 1931 and the full-scale war with China in 1937. At the same time, Tokyo’s aggression alarmed Washington, leading to sanctions that helped precipitate Japan’s attack on Pearl Harbor in 1941. The Pacific War that followed ended with Japan’s catastrophic defeat and U.S. occupation.

In the post-war years, Washington sought to rebuild Japan as a bulwark against communism. The 1951 U.S.-Japan Security Treaty formalized America’s military presence in the country, even as Japan adopted a pacifist constitution under Article 9, renouncing war as a means of settling disputes. While this kept Japan’s defence policy restrained for decades, the growing threats posed by China and North Korea have forced Tokyo to rethink its strategic stance.

Japan’s security doctrine has undergone a radical transformation in recent years. Former Prime Minister Shinzo Abe spearheaded efforts to reinterpret the country’s pacifist constitution, enabling its Self-Defence Forces (SDF) to play a more active role in collective defence. Under Prime Minister Fumio Kishida, Tokyo has further deepened military ties with the U.S., committing to a record increase in defence spending and bolstering its capabilities to counter Chinese aggression in the East China Sea and the Taiwan Strait.

Hegseth’s recent announcement of a “war-fighting headquarters” in Japan is the latest indication of this shift. The upgraded U.S. military command in Japan, coupled with the launch of the Japan Joint Operations Command (JJOC), signals a move toward greater operational integration between the two allies. Washington and Tokyo are also expanding joint missile development, strengthening logistical support for warships and aircraft, and enhancing Japan’s military presence on its southwestern islands - strategic areas near Taiwan and disputed waters with China.

These moves are a direct response to China’s increasing assertiveness. Beijing’s military build-up, frequent incursions into Japan’s airspace, and its growing naval presence in the Pacific have alarmed policymakers in both Tokyo and Washington. China’s claims over Taiwan, a potential flashpoint for U.S.-China confrontation, have further galvanized Japan to step up its military preparedness. As Hegseth bluntly put it, Japan would be on the frontlines of any conflict in the western Pacific.

The deepening of U.S.-Japan military cooperation marks a historic shift, but entails risks. Japan’s military resurgence has provoked criticism from China, which views Tokyo’s strategic realignment as part of a broader U.S. effort to encircle and contain Beijing. The prospect of Japan playing a more active role in regional conflicts, particularly in a Taiwan crisis, also raises concerns about escalation.

At the same time, Japan remains wary of America’s long-term commitment. The Trump administration’s “America First” policy and threats of trade tariffs has unsettled Tokyo, prompting concerns about the reliability of the alliance. While Hegseth’s reassurances reaffirm Washington’s focus on the Indo-Pacific, Japan has been hedging its bets by diversifying its defence partnerships, strengthening security ties with Australia, India and NATO countries.

While the U.S.-Japan alliance remains the bedrock of security in the Pacific, its transformation underscores that the era of Japan’s post-war pacifism is over. As China flexes its military muscles, Japan - once America’s fiercest enemy - is emerging as one of its most indispensable allies in maintaining regional stability.