Over the past two weeks, U.S. President Donald Trump, Vice President JD Vance and other U.S. leaders have threatened a dramatic shift in U.S. foreign policy. In a series of statements that could upend decades of ties between the United States and Europe, the Trump administration has indicated that Washington will no longer guarantee European security, most significantly regarding the threat from a revanchist Russia with which Washington is now seeking greater alignment — a pronounced about-face in U.S. foreign policy. Trump and other top U.S. officials had already made many public statements calling into question the strength of trans-Atlantic ties, not least by aggressively pushing to take territory from NATO ally Denmark and rebuking multiple European leaders while praising their far-right political challengers.

Europe is hardly the only continent on the receiving end of U.S. foreign policy shocks. In barely a month since taking office, the Trump administration has thrown decades of traditional U.S. foreign policy positions into flux. Among other things, Trump threatened tariffs on the two largest U.S. trading partners, Canada and Mexico, floated the idea of forcibly retaking the Panama Canal, promoted a plan to carry out what many observers say amounts to ethnic cleansing in the Gaza Strip, effectively suspended U.S. civilian foreign aid, and castigated many of the norms, rules and institutions that have provided the foundation for the U.S.-dominated, Western-led global order since the end of World War II.

While time will tell whether these and other developments are more bark than bite, Trump's rhetoric and actions thus far indicate he is serious about dramatically changing U.S. foreign policy to the extent that we as analysts must now ask, is the United States now a revisionist power? If so, a revisionist America could open a path to a more stable world order. It would be much more likely, however, to lead to one of greater uncertainty, volatility and conflict amid a return to multipolarity.

Great Power Politics

In a simplified version of international relations theory, powerful states can be roughly divided into two categories: status quo and revisionist powers. Whereas the former seek to preserve the existing international order, the latter aim to challenge it. Examples of revisionist powers throughout different periods of modern history include Napoleonic France, Imperial Germany and the Soviet Union. Today, at least until recently, it is China and Russia that have chiefly received this moniker — one that the first Trump administration used in its 2017 National Security Strategy — as they have presented the clearest intent and capability to challenge the post-World War II global order. Beijing and Moscow are more aligned in their opposition to what they see as a Western-led international system than in a shared vision for what should replace it. But despite their differences and even as they have tried to exploit the current global order for their own benefit, they have each sought to significantly revise, if not completely end, the existing order.

By contrast, the United States has not merely benefited from the post-World War II order, but since then has been the driving force supporting it. In the wake of the war, the United States by far has been the economically and militarily strongest Western power, leveraging those strengths to rebuild Europe (and Japan) and create a new rules-based global governance framework based on economic liberalism and democratic politics. Supported by its Western allies, the United States drove the creation of multinational institutions like the World Bank, International Monetary Fund and what became the World Trade Organization, helping to cement Western, and especially U.S., economic influence. Meanwhile, the United States spearheaded the creation of the United Nations, created military alliances like NATO, and broadly facilitated deeper integration among friendly states. Inevitably, these actions did not go unchallenged by the Soviet Union, but the United States and its allies weathered the threat of its communist statism. And following the end of the Cold War, a victorious United States ushered in a unipolar moment in which a U.S.-led world order appeared to reign supreme.

But it was just a moment. By the early 2000s, and certainly by the 2010s, the world was steadily becoming multipolar once again. China led this pushback, but a host of middle powers — ranging from South Africa to Turkey — also increasingly pulled at the foundations of the Western-led global system. Despite close ties with the United States, even the European Union established itself as another pole with interests that did not always align with U.S. interests. And Washington itself contributed to the erosion of the global system it had dominated with actions like invading Iraq and retreating from what had been stalwart support for free trade.

Trump's rhetoric and actions thus far, however, point toward a fundamental shift in U.S. foreign policy. For whatever role past U.S. administrations, including the first Trump administration, have had in eroding the U.S.-led global order, Trump's current presidency seems to mark a turning point. Trump is a self-described opponent of what he calls globalism, and his policy preferences contradict nearly every aspect of the post-World War II order that has traditionally aligned with the broad contours of U.S. foreign policy across past administrations, ranging from his mercantilist trade agenda to his skepticism, if not scorn, of multilateral institutions and alliances (including those dominated by the United States). In Trump's view, the current global order is stacked against the United States, facilitating massive freeriding and requiring a decisive break to enable the country to return to its ruthless pursuit of self-interest abroad and focus on development at home.

A Trumpian New Order

A potentially revisionist United States need not automatically cause disarray in the international system. Though they may not share Trump's precise complaints, countries across the globe increasingly feel that the current global governance architecture is no longer fit for purpose. Be it the exclusivity of the permanent members of the U.N. Security Council — not coincidentally, the victors of World War II (China, France, Russia, the United Kingdom and the United States) — the internal paralysis that has debilitated the World Trade Organization, or more generally the liberal economic and democratic political values baked into Western-led institutions, many states in the so-called Global South perceive at best hypocrisy when the West flouts these norms and at worst a deliberate, vaguely neo-imperialist, effort to prevent their rise.

From this perspective, a U.S. president clearly willing to shake things up opens the door to global governance revisions that could lessen at least some of these complaints and perhaps even bring greater global stability. For instance, better relations between Washington and Moscow could reduce global friction on a host of issues, potentially even resulting in some sort of grand bargain to adjust how multilateral institutions function and establish new, more stable norms for the 21st century to confront Beijing. Meanwhile, an America that cares less about promoting democratic values and retreats from parts of the globe may actually remove irritants in Washington's bilateral relations with multiple states if they no longer have to navigate U.S. demands about their liberal credentials and geopolitical alignment, reducing geopolitical frictions. And in general, a United States that intervenes less to uphold a global order could enable regional and subregional blocs to become more powerful if they fill the void, potentially bringing greater stability to different parts of the world.

There are also scenarios in which America First clearly succeeds or fails, both of which could result in greater stability over time. These are speculative, but it is important to consider the more extreme (and less likely but more impactful) versions of each side of the coin. In the first, Trump's unconventional foreign policies achieve their goals, leading to various developments that could include:

• The collapse of the Iranian regime brings greater stability to the Middle East as Israel and Arab states more openly cooperate with less fear of blowback.
• A global pressure campaign against China (including support from a Russia that is closer to the United States and more wary of China's growing influence in Central Asia, traditional U.S. allies in East Asia like Australia and Japan, and an India that is pushed closer to the West amid frictions with China) that succeeds in balancing against Chinese expansion, reducing the likelihood of conflict in the Indo-Pacific.
• A sufficiently strong spark for European states to overcome divisions to deepen political, economic and, perhaps most important, security ties that ultimately result in a more secure Continent.

Alternatively, what is America's loss is the world's gain. In this scenario, Trump's aggressive foreign policies alienate most other countries, leading much of the rest of the world to greater cooperation in a new global system that excludes the United States and is more stable because of it. This could lead to:

• Europe, China, India and others rewriting global trading rules that better address the current global landscape.
• Countries across the Global South drawing closer together to reform international institutions to make them more relevant to their needs.
• The rise of regional hegemons better enforcing rules and balancing competing interests in their areas of influence, but without intruding into those of others.

Might Makes Right

While the aforementioned outcomes are possible, the much more likely result of a potentially revisionist United States is a world with more uncertainty, volatility and conflict. In this forecast, the effective end of the post-World War II order would not catalyze greater stability by incentivizing states to better collaborate to construct a more effective international structure. Instead, it would return the global system to an unstable multipolarity amid what international relations theorists refer to as anarchy in the sense of the lack of a supreme hegemon whose coercive power can bring order. As Thucydides wrote millennia ago, in such a world, the strong would do what they can and the weak would suffer what they must.

The historical record and signs thus far already indicate that such an unstable world is emerging, though the implications would take many years, if not decades, to fully play out. To begin with, the lack of an enforced global governance architecture would breed uncertainty that ripples across global politics, economics, security and other dynamics over the course of the 21st century. Over time, expectations for state behavior would change dramatically, ushering in much greater unpredictability for everything from trade talks to military operations. Powerful states would feel even less restrained by fears of blowback, while weak states would be increasingly coerced by others with more resources and leverage. More immediately, China and Russia would be more likely to pursue their expansionist, coercive agendas in their near-abroad as military alliances like NATO wither and institutions like the United Nations are powerless. And, over time, a host of middle powers like India and the United Arab Emirates would likely pursue aggressive foreign policies with greater abandon. These dynamics would result in more frequent crises — both deliberately created and due to increasingly common miscalculations — which would also take longer to resolve given that there is no longer a global governance system capable of unifying states increasingly focused on self-preservation.

Over time, the further erosion of an international order that had promoted liberal economics and democratic politics — combined with the return to unstable multipolarity amid the lack of a hegemon capable of enforcing a new order — would usher in even more intense nationalism across the globe as states revert to their protectionist tendencies and authoritarian governance would become more attractive to populations seeking strongmen they believe will protect their country's interests. Over decades, this shift would significantly alter global trade — restructuring supply chains and the financial system, among other things — and lead to much higher risks of interstate conflict, particularly amid what would likely be multiple arms races as countries scramble to shore up their capabilities as they increasingly doubt foreign promises to come to their defense. This would occur not only among great powers that would be more unabashed in pushing their weight around but also among smaller states that would believe they could get away with foreign conquests without serious blowback. The same would go for intrastate violence, particularly in fragile states that had previously depended on foreign help (or coercion) to tamp down the risks of civil conflict.

These and other disruptive developments are not meant to suggest that there would be no cooperation across state lines, but rather that such collaboration itself would be destabilizing. Without a global hegemon willing and able to uphold, let alone recreate, a new order, proliferating miniblocs would divide up the world, a further hallmark of a return to an unstable multipolarity. These may be organized by geography, e.g., at a regional or subregional level, or by shared interests, such as so-called coalitions of the willing. Together, they would mark a clear shift from large, deep alliance structures and toward much more limited and transactional approaches. These miniblocs would be constantly shifting and often beset by competition among participants for influence, meaning they would not only be less stable, but also much more unlikely to look beyond their geographic or functional focus to enforce order abroad.

Unchartered Revisionism

Ultimately, what makes the current moment unique is that the revisionist U.S. impulse is against an international system it has constructed, upheld and, at least according to conventional wisdom, strongly benefited. Past global order transitions — even when Washington took over from London in the mid-20th century, the only peaceful transition of hegemonic power in history — have not seen the reigning hegemon willingly turn against the order it had created and nurtured.

As a result, the precise outcome of a potentially revisionist America is not predetermined. With the global order already under intense strain, further developments that lead to its complete end would at least offer the opportunity to construct a new international system better suited to the 21st century. Yet there does not appear, at least for the foreseeable future, to be a supreme power both willing and able to supplant the United States, meaning that a reversion to a fractious multipolar world is far more likely. Thus, the next few years seem likely to be more uncertain, volatile and full of conflict. The bigger question appears to be whether the ultimate outcome of this disorder compels a new attempt at rebuilding a global order later this century or whether anarchy prevails well beyond the foreseeable future.