Robert Kagan, a senior fellow at the Brookings Institution, is widely regarded as one of the most influential American analysts in international affairs. He is traditionally associated with the neoconservative camp and with proponents of liberal internationalism—an approach rooted in the belief that the values of democracy, liberalism, and the free market must be spread, including through the use of force, until they become universal. In the past, Kagan was a member of the Republican Party, but he left it in 2016 after Donald Trump became the party’s presidential nominee. In an article for The Atlantic, he argues that by early 2026 Trump had effectively dismantled the “U.S.-led liberal international order.” In its place, Kagan suggests, a multipolar system is taking shape—one that carries significantly higher risks both for the United States itself and for international stability as a whole.
The collapse of the liberal international order, Kagan argues, was not the result of the United States losing the capacity to sustain it, but rather of the United States—or more precisely, Donald Trump—deliberately abandoning the role of guarantor of global security that the country assumed after World War II. This was not a matter of forced decline, but of political choice.
The emerging multipolar system, Kagan warns, will increasingly resemble the world before 1945—with constant great-power rivalry, a succession of conflicts and wars, and a steady rise in military spending. Competition for resources, which in recent decades has been largely economic in nature, will once again shift into the military realm: the primary struggle will no longer be over markets, but over territory.
American society, he emphasizes, is not prepared for such a future. For nearly eighty years, it has lived in conditions of relative security and comfort, underpinned by a global network of alliances, free trade, and a system of international arrangements built around U.S. dominance.
Historically, multipolar international systems have almost inevitably produced wars. Kagan points to the nineteenth-century “Concert of Europe,” which emerged after the Napoleonic Wars and lasted until World War I. It rested on a balance of power among Britain, France, Prussia or Germany, Austria, and Russia and did indeed prevent a continent-wide conflict for decades. Yet the period was marked by numerous local wars—from the Crimean War of 1853–1856 to the Franco-Prussian War of 1870–1871—each claiming hundreds of thousands of lives and leading to the redrawing of borders. The two world wars of the first half of the twentieth century were likewise the outcome of rivalry among great powers and their blocs.
The order that took shape after 1945, largely through U.S. efforts, was, in Kagan’s view, a deliberate attempt to break out of this vicious cycle. The United States suffered comparatively little in the world wars, and geography—oceans on both sides—shielded it from direct competitors. Under these conditions, it assumed responsibility not only for its own security, but for the security of the international system as a whole.
Washington contained the rise of regional hegemons in both Europe and Asia, pressing would-be challengers to abandon expansionist ambitions. The United States, Kagan argues, generally favored not the direct conquest of territory and resources, but the binding of other states through alliances, trade, investment, and other instruments of soft power.
In the standard logic of international relations, states band together against any power seeking dominance. Yet after World War II, that did not happen. Even after recovering, countries such as Britain, France, Germany, and Japan did not challenge American hegemony; they accepted it—often at the cost of renouncing their own ambitions. At the core was a “grand bargain”: allies trusted the United States on the assumption that it would guarantee their security and would not use its preponderance to exploit partners, but would instead help them prosper. That understanding delivered decades of relative stability, including through the Cold War, while also constraining Russia and China’s ability to overturn the existing order.
With Trump’s arrival, Kagan notes, this framework began to unravel. The president argues that providing security for allies is too costly and demands excessive effort from the United States; claims that partners are exploiting the system of free trade at America’s expense; and himself advances territorial claims against other countries. In doing so, the author contends, the United States is violating every core element of its own “grand bargain.”
Under these conditions, Europe and Asia will find themselves squeezed between hostile great powers and will be forced to rearm and to turn into independent centers of power. This, Kagan predicts, will fuel a resurgence of nationalism, a new arms race, and a proliferation of conflicts. Germany, Japan, Poland, France, South Korea—all of them, deprived of the American security guarantee, will be compelled to “become normal,” that is, to compete for regional or global status, including through military means.
The world will thus once again become a realm of hard-edged competition for resources, security, and spheres of influence. The concept of spheres of interest, which policymakers sought to abandon after World War II, will return as one of the primary sources of conflict. Small and medium-sized states will once again be confronted with a choice between submission and war.
In the end, Kagan concludes that by dismantling the system of alliances and undermining the United States’ moral authority, Trump is turning the country from a global leader into an international outcast.
American power, he stresses, has always rested not only on military and economic strength, but also on the trust of partners—on the perception of the United States as a power that does not act solely out of narrow self-interest. That foundation, in his view, has been eroded. And if sustaining the liberal international order seemed too costly to Americans, the price of the world that replaces it will prove immeasurably higher.