20 March 2026
The recent strikes on Iran and the divided European responses reveal more than a regional crisis. They expose a deeper theoretical shift in world politics. This matters because it shapes how countries make decisions about war, alliances, and economic cooperation, issues that directly affect global stability, markets, and security. While several European leaders criticized the strikes from a liberal perspective, defending international law, others used realist language, signalling deterrence logic. This divergence illustrates a broader movement from liberal internationalism (cooperation through institutions) toward realism (states prioritizing power and security). Drawing on Acharya (2018), Ikenberry (2018; 2024), and Mearsheimer (2019), I argue that structural realism, as formulated by Waltz (1979), offers the most coherent framework for understanding both the erosion of liberal hegemony and the strategic logic behind contemporary great-power behaviour.
Acharya’s central claim is that the American World Order (AWO) is ending, regardless of whether U.S. material power is in absolute decline (Acharya, 2018, pp. 1–2). He demonstrates that the liberal order was geographically limited, coercively enforced, and ideologically overstated (pp. 49–54). He argues that the unipolar moment has passed due to both internal overreach and external power shifts (pp. 22–23, 42). His “multiplex world” describes a decentralized system with multiple actors, dense interdependence, and diversified governance (pp. 8–9, 16–17). In practice, this means no single country dominates. Instead, multiple powers and regional organizations shape outcomes.
Even though Acharya’s framework explains the decline of liberal hegemony and the diffusion of authority, but it does not offer a structural theory of how states will behave under conditions of anarchy. What do states actually do when tensions rise? As we’ve seen in recent months they deter, balance, or use force. By rejecting polarity debates as analytically limiting (pp. 11–12), Acharya distances himself from structural realism. However, the Iran case suggests that polarity and material power still matter. When the United States and Israel strike Iranian targets, they are not acting within a multiplex governance experiment, but are responding to security calculations shaped by deterrence, regional balance, and alliance credibility. Acharya explains the erosion of the old order, but less clearly how power politics structures outcomes.
Ikenberry offers a more optimistic defence of liberal internationalism. In 2018, he frames the decline of the liberal order a crisis caused by the backlash against globalization’s rapid expansion generated by the success and overexpansion of liberal globalization rather than by renewed great-power rivalry (Ikenberry, 2018, p. 10). Liberal internationalism, he argues, can survive if it undergoes domestic renewal and institutional reform (pp. 22–23). In 2024, he doubles down, portraying liberal statecraft as a two-century tradition of institutional problem-solving aimed at mitigating anarchy, hierarchy, and interdependence (Ikenberry, 2024, pp. 235–236, 243–244).
The current Iran case underscores the limits of this institutional optimism. When security stakes rise sharply, institutional coordination gives way to strategic alignment. European governments defend international law, yet some accept force to maintain deterrence. This gap between normative commitment and strategic behaviour supports Mearsheimer’s claim that the liberal order was only sustainable under unipolarity (Mearsheimer, 2019, pp. 12–13). Once China’s rise eroded U.S. dominance, great-power competition returned, and liberal aspirations collided with nationalist and security imperatives (pp. 41–44).
Mearsheimer’s argument is stark: the liberal international order was “bound to fail” because it attempted to transcend nationalism and balance-of-power politics (p. 7). Democracy promotion backfired, supranational governance clashed with domestic sovereignty, and hyperglobalization empowered China (pp. 31–41). The outcome is a world of competing realist orders (pp. 43–44). The Iran strikes fit this logic. They reflect deterrence signalling, alliance management, and the prevention of regional hegemony which are core realist concerns.
Here, Waltz’s neorealism (1979) provides the crucial theoretical anchor. He argues that anarchy incentivizes states to prioritize survival and balance against threats. Unlike liberalism or constructivism, realism offers a parsimonious structural explanation grounded in the distribution of capabilities. Whether leaders invoke international law or liberal norms is secondary; what matters is how power is distributed and how states respond to systemic constraints. In other words, states don’t get to choose whether to care about power, because the system forces them to.
The European reactions to Iran demonstrate this structural pull. Normative language persists, but strategic calculation dominates. As U.S. unipolarity fades, allies hedge, balance, and recalibrate. The shift is not ideological change but an adaptation to reality. Acharya is right that the AWO is ending. Yet his multiplex vision underestimates the enduring centrality of power competition. Ikenberry is right that institutions matter, but he overstates their autonomy from material power. Mearsheimer and Waltz better capture the structural forces driving behaviour.
The Iran crisis thus illustrates a broader transformation: the erosion of liberal hegemony is not producing a post-power world of shared governance but a reversion to realist dynamics under new polarity structures. Realism does not deny the existence of institutions or norms; it explains their limits. As the liberal order fragments and strategic rivalry intensifies, realism remains the most structurally coherent theory of world order. The power of realist theory lies not in its normative appeal, but in its explanatory power. The ongoing events surrounding Iran make this difficult to dismiss.
Bibliography
Ikenberry, G. J. (2018). The end of liberal international order? International Affairs, 94(1), 7–23. https://doi.org/10.1093/ia/iix241
Ikenberry, G. J. (2024). Liberal statecraft and the problems of world order. Oxford Review of Economic Policy, 40(2), 234–245. https://doi.org/10.1093/oxrep/grae020
Mearsheimer, J. J. (2019). Bound to fail: The rise and fall of the liberal international order. International Security, 43(4), 7–50. https://doi.org/10.1162/isec_a_00342
Acharya, A. (2018). The end of the American world order (2nd ed.). Polity Press.
Waltz, K. N. (1979). Theory of international politics. McGraw-Hill.