South Korea's 'middle power' moment has arrived — will it seize it?

For decades, South Korea has occupied an ambiguous position in the international order — too powerful to be dismissed as a small state, yet constrained by security dependence. The fracturing of American hegemony, the emergence of a more complex geopolitics and the growing assertiveness of non-Western nations have together created what may be the most significant opportunity for middle power diplomacy in a generation. The question is whether Seoul has the vision — and the domestic political will — to seize it.

To understand South Korea’s opportunity, we must first understand the world it inhabits. Analysts routinely describe today’s international order as “fragmented” or “multipolar,” but both terms fall short. Fragmentation implies breakdown and multipolarity implies a simple distribution of power among a handful of great powers. Neither captures reality.

As I have explained in my new book, "The Once and Future World Order" a more appropriate concept is multiplexity — a world of overlapping institutions, diverse actors and complex interdependencies, where no single power or a handful of powers dictate the rules and where complexity, rather than being a problem to be solved, is an enduring condition to be navigated creatively. In a multiplex world, great powers still matter — but unlike in a classic multipolar system, they do not monopolize influence. Middle powers, corporations, regional organizations and non-state actors all shape outcomes in ways that a purely "great power" lens cannot capture.

This matters for South Korea because the category of “middle power” is itself in the midst of a historic transformation. For most of the Cold War and early post-Cold War era, middle power diplomacy was largely a Western enterprise. Australia, Canada and Norway led the charge by championing multilateralism, pioneering the concept of human security and advancing the responsibility to protect. Their brand of middle power activism was reformist in orientation: working within the liberal international order to improve and extend it. Today, some of the most consequential middle powers increasingly hail from the Global South, like Indonesia, Brazil, South Africa and other actors outside of the Western alliance system. At the same time, non-Western nations allied to the U.S. such as Turkey and South Korea have genuine middle power credentials, operating in a more crowded, competitive and ideologically diverse field.

This evolution carries real consequences. Middle powers are no longer a homogenous bloc united by a commitment to liberal norms. Some remain firmly reformist, while others have grown openly revisionist, challenging the very order their predecessors sought to refine. Some are closely tied to the United States security umbrella, and others deliberately cultivate strategic autonomy. South Korea falls clearly in the first camp. It possesses consequential military and industrial capacity — a world-class defense industry, a technologically sophisticated export-oriented economy and growing diplomatic reach. But it remains dependent on Washington for security guarantees against North Korea. This distinguishes Seoul sharply from Jakarta, Brasília or Pretoria, none of which carry the same burden.

That dependence is not merely a security constraint. It is a political one. South Korea’s ability to exercise independent middle power diplomacy to build coalitions, broker agreements or pursue initiatives that Washington may not prioritize is perennially shaped by the question of how far it can move without straining the alliance. Under a “rules-based liberal order” with a predictable American hegemon, that tension was manageable. Under Donald Trump, it has become acute. The Trump presidency has exposed what might be called the “fatal attraction” of hegemonic dependence: the vulnerability of states that have outsourced too much of their strategic thinking to an outside power that may, at any moment, change its mind. For South Korea, this is not an abstract lesson. It is an existential one.

Middle power diplomacy also faces a challenge that its advocates too rarely acknowledge: competition among middle powers themselves. The history of middle power relations is not simply one of solidarity and multilateral cooperation. Qatar and Saudi Arabia have clashed bitterly. Australia and Canada competed for leadership in Asia-Pacific multilateralism during the 1990s. Indonesia and Malaysia disputed the intellectual ownership of regional security concepts during the same era. Japan and South Korea — natural partners in many respects — share a relationship marked as much by historical mistrust as by cooperation. Any realistic account of South Korea’s middle power strategy must reckon with these rivalries, not paper over them.

Domestic politics adds yet another layer of complexity. The current multiplex order creates more room for middle power autonomy than at any point in recent decades. But governments do not automatically exploit that room. Ideological alignment with great powers, electoral calculations, and nationalist pressures all constrain how boldly a middle power government is willing to act. South Korea’s middle power role has historically fluctuated with the ideological leanings of whoever holds the presidency. This inconsistency is itself a strategic liability. What Seoul needs is a durable domestic consensus on the nature and purpose of its international role that can survive changes in government and outlast any single presidency.

So what should South Korea actually do? The answer lies in sustained, creative investment in the institutions and relationships that give middle powers their leverage. The United Nations remains an underutilized platform, but the more important frontier is regional. Here, South Korea has precedent to draw on: In the late 1990s and early 2000s, Seoul was a driving force behind East Asian cooperation, contributing intellectual energy to the East Asian Vision Group and the East Asian Study Group that laid the groundwork for the East Asian Summit in 2005. That initiative demonstrated that South Korea could shape the regional architecture.

That capacity has not disappeared. What may have diminished is the ambition. A multiplex world will not wait for middle powers to get comfortable. The states that shape the next order will be those willing to make bold choices — to diversify foreign policy alignments, invest in regional institutions and build coalitions that do not require Washington’s blessing at every step.

South Korea’s middle power moment is real. The window, however, will not remain open indefinitely.

Amitav Acharya is a Distinguished Professor at American University, Washington D.C., and author of "The Once and Future World Order: Why Global Civilization Will Survive the Decline of the West" (Korean translation by Book21). This article is based on his presentation at the 2026 Jeju Forum for Peace and Prosperity.