A world without U.S. hegemony is a world of great power competition and militarization.

Thanks to the U.S.-led order, for decades, most countries have not had to fight for market access, guard their supply chains, or even seriously defend their borders. The U.S. Navy has kept international waterways open, the U.S. market has provided reliable consumer demand and capital for dozens of countries, and U.S. security guarantees have covered nearly 70 nations. Such assurances have benefited everyone: not just Washington's allies and partners but also its adversaries. U.S. security guarantees had the effect of neutering Germany and Japan, the main regional rivals of Russia and China, respectively. In turn, Moscow and Beijing could focus on forging ties with the rest of the world rather than fighting their historical enemies. Without U.S. patronage and protection, countries would have to get back in the business of securing themselves and their economic lifelines.

Such a world would see the return of great-power mercantilism and new forms of imperialism. Powerful countries would once again try to reduce their economic insecurity by establishing exclusive economic zones, where their firms could enjoy cheap and secure access to raw materials and large captive consumer markets. Today, China is already starting to do this with its Belt and Road Initiative, a network of infrastructure projects around the world; its "Made in China 2025" policy, to stimulate domestic production and consumption; and its attempts to create a closed-off, parallel Internet. If the United States follows suit, other countries will have to attach themselves to an American or a Chinese bloc – or forge blocs of their own. France might seek to restore its grip on its former African colonies. Russia might accelerate its efforts to corral former Soviet states into a regional trade union. Germany increasingly would have to look beyond Europe's shrinking populations to find buyers for its exports -and it would have to develop the military capacity to secure those new far-flung markets and supply lines, too.

As great powers competed for economic spheres, global governance would erode. Geopolitical conflict would paralyze [inhibit] the UN, as was the case during the Cold War. NATO might dissolve as the United States cherry-picked partners. And the unraveling of the U.S. security blanket over Europe could mean the end of the European Union, too, which already suffers from deep divisions. The few arms control treaties that remain in force today might fall by the wayside as countries militarized to defend themselves. Efforts to combat transnational problems-such as climate change, financial crises, or pandemics--would mimic the world's shambolic response to COVID-19, when countries hoarded supplies, the World Health Organization parroted Chinese misinformation, and the United States withdrew into itself.

The resulting disorder would jeopardize the very survival of some states. Since 1945, the number of countries in the world has tripled, from 46 to nearly 200. Most of these new states, however, are weak and lack energy, resources, food, domestic markets, advanced technology, military power, or defensible borders. According to research by the political scientist Arjun Chowdhury, two-thirds of all countries today cannot provide basic services to their people without international help. In short, most countries depend critically on the postwar order, which has offered historically unprecedented access to international aid, markets, shipping, and protection. Without such support, some countries would collapse or be conquered. Fragile, aid-dependent states such as Afghanistan, Haiti, and Liberia are only some of the most obvious high-risk cases. Less obvious ones are capable but trade-dependent countries such as Saudi Arabia, Singapore, and South Korea, whose economic systems would struggle to function in a world of closed markets and militarized sea-lanes.