On July 1, 2014, Japanese prime minister Shinzo Abe and his Cabinet engaged in a dramatic constitutional reinterpretation. Traditionally, Japan’s constitution had been read as imposing pacifism on the country: Japan could not engage in military force except in absolute self-defense. But under Abe’s new reading, the constitution would grant Japan the right to engage in collective self-defense—in other words, to come to the aid of allied forces under attack even if Japan itself is not targeted.

This update may seem minor when set alongside the robust military campaigns launched by other nations like the United States. But for Japan, Abe’s reinterpretation represents a significant shift away from the island-nation’s postwar pacifism—a shift that will have important and largely beneficial consequences for the U.S.-Japanese alliance. By the end of the year, the two states will release revised Guidelines for Defense Cooperation, which will build in part on Prime Minister Abe’s constitutional reinterpretation and update the framework that governs the U.S.-Japanese alliance in times of both peace and war.

But while the United States has applauded his reinterpretation for strategic reasons, Abe has faced persistent opposition at home. For his domestic critics, the constitution enshrines a pacifist principle forged in the blistering fires of World War II. It should not be tossed aside lightly, and the Abe administration has failed to explain how its reinterpretation accords with the lessons of history.

In order to succeed, Abe will be forced to navigate between strategic and historical currents that often tug in opposite directions. Reconciling these competing forces is possible, but only if the Abe administration can convey to a skeptical public that collective self-defense aligns with Japan’s pacifist principles, rather than its militaristic past. For the most part, this debate will unfold domestically, but the United States should intervene on the margins by clarifying the strategic benefits of the reinterpretation for the alliance and by urging the Abe administration to shy away from historically revisionist rationales.

A Constitution That Changes with the Times

As World War II ended, the United States occupied Japan and set about deconstructing its militaristic government. As part of this demolition effort, Washington revamped Japan’s legal system and sought to ensure that Tokyo could never again lawfully threaten regional peace.

The result was Article 9 of the newly minted Japanese Constitution. The first clause announced that “the Japanese people forever renounce war as a sovereign right of the nation and the threat or use of force as means of settling international disputes.” To serve this aim, the second clause continued, “land, sea, and air forces, as well as other war potential, will never be maintained.”

Yet almost as soon as it was adopted, Article 9 came under severe strain. Many understood the clause to prohibit the creation of any military force whatsoever. But two years after the new constitution was ratified, Japan faced a security crisis. The Chinese Communist Party had taken control of the Chinese mainland, and faced with a resurgent communist threat in Asia, the United States was asking Japan to help ensure regional security. For the remainder of the Cold War, Washington would continue to pressure its ally to rearm and play the role of security provider.

This pressure influenced how Japan has interpreted Article 9. For instance, once the Korean War broke out, the United States relocated forces from Japan to the Korean Peninsula, robbing the island nation of its principal shield against potential attackers. In response, Japan organized a robust, national police force that could defend the country in a time of need. Within a few years, the Diet reorganized these defense capacities and created the Japanese Self Defense Forces (JSDF)—a military in all but name. Faced with a lurking constitutional issue, the Japanese Cabinet squared the existence of the JSDF with Article 9 in late December 1954 by arguing that “[t]he Constitution did not deny the self-defense right; Japan renounced war, but did not renounce the right to struggle in order to defend itself.”

Two important lessons emerge from this episode. First, Tokyo justified its rearmament by emphasizing mission over capability. In other words, the JSDF looked like a conventional military in many respects, but—crucially—it would be used only for the narrow purpose of self-defense. Second, this limited mission would shape the division of labor in the U.S.-Japanese alliance. As one scholar has put it, the JSDF’s focus ensured that “the United States would provide offensive capability and the SDF would concentrate on the less likely and smaller scale impact of any spillover effects from regional conflicts.”

In recent years, however, both assumptions have lost much of their force. First, Japan may no longer be able to stand at the periphery of a regional conflagration; instead, it is much more likely to find itself caught in the middle. Although in past years Tokyo could safely watch the United States battle in the Taiwan Strait or on the Korean Peninsula, today, Japan cannot sit out a potential crisis with China over the Senkaku Islands, or a nuclear launch from North Korea. In part, Japan is the victim of technological development: countries like China and North Korea are gaining access to long-range military capabilities that expand the potential theater of conflict, roping in the Japanese islands. Whether Tokyo likes it or not, the fight is increasingly being brought to Japan itself. The upshot is that to defend itself, the island-nation must become more proactive: it must work closer with its regional allies and recognize that potential threats may now come from farther afield.

In light of these trends, Abe and his Cabinet reinterpreted Article 9 on July 1, 2014, in a way that would allow Japan’s military to engage in collective self-defense. Although Abe highlighted Japan’s status as a “peace-loving nation,” he also recognized that “[t]he peace we enjoy today is not bestowed upon us by someone else. The only way to achieve it is to establish it with our own hands.” This responsibility implies the continuing need to “respond to the changes in the times.” Abe stressed how Article 9 had previously been reinterpreted in order to allow past changes in the JSDF’s mission, including a revision of the U.S.-Japanese alliance in 1960 and Japan’s participation in UN peacekeeping operations since the end of the Cold War. In light of Japan’s “increasingly severe” threat environment, the Cabinet had decided to act once again.

A Walk Down Memory Lane

Yet despite the strategic impetus behind its reinterpretation, the Abe administration is still facing widespread popular opposition to its nationalist policies. In a poll conducted less than two weeks before Prime Minister Abe’s announcement, the Japanese public largely opposed exercising the right to collective self-defense (56 percent), while only a small minority supported it (28 percent). Activists have peppered the Japanese press with anti-reinterpretation editorials, and in one extreme case, a man set himself on fire to protest the decision. These protests have affected Abe’s approval ratings: after the decision was announced, they tumbled to a historic low of 42 percent.

In part, this opposition reflects a deep-seated pacifist culture, a collective national memory of the horrors Japan visited upon its neighbors during World War II—as well as the horrors it reaped in return. This memory has kept Japan’s martial impulses in check for almost seven decades, and it is deeply ingrained into the psyche of the nation. To its supporters, Article 9 is what justifies the country’s exceptionalism: Japan, the only nation to renounce war in its constitution. It is also a considerable source of pride—a little more than a month ago, some experts suggested that this year’s Nobel Peace Prize might be awarded to “the Japanese people, who have abided by Article 9 and have not waged war in nearly 70 years.” (Prime Minister Abe must have breathed a sigh of relief when Japan lost.)

Of course, it is not clear that the reinterpretation of Article 9 runs afoul of these engrained pacifist principles. To be sure, the reinterpretation broadens the context in which Japan might become involved in conflicts outside of its borders. But as a practical matter, the reinterpretation also serves second-order purposes that may deter the prospect of a conflict in the first instance. As Abe has pointed out, “these preparations will themselves serve as a great deal of power that deters such contingencies from occurring.” Unsurprisingly, the Romans put it best centuries ago: Si vis pacem, para bellum. If you want peace, prepare for war.

Not only does the reinterpretation of Article 9 grant the JSDF greater flexibility, but it also removes a persistent source of friction in the U.S.-Japanese alliance. If Japan is unwilling to lift a finger to prevent Chinese strikes on American vessels until Japan itself is attacked, then Tokyo is right to worry about the long-term American commitment to defend the Senkaku Islands. In the most crude terms, a one-way alliance is not much of an alliance at all. And without the U.S.-Japanese alliance, Tokyo would be caught at sea in a region rife with crises threatening to explode into war.