On the night of January 17, 1991, television viewers around the world watched something they had never seen before. Against the backdrop of a black sky illuminated by antiaircraft fire, American precision-guided bombs slammed into windows, air shafts, and command bunkers in Baghdad. CNN broadcast the Gulf War live. For millions of people, the images seemed to herald the arrival of a new age.

To understand why those images mattered, it is necessary to remember how threatening Iraq seemed before the war began. Iraqi dictator Saddam Hussein commanded nearly one million armed men. His army had survived eight years of brutal war with Iran and possessed one of the largest tank forces in the world. Iraq’s invasion of Kuwait raised fears that Saddam would soon turn his forces on Saudi Arabia, potentially making his country an oil hegemon in the Persian Gulf and placing a quarter of global oil supplies under his direct control.

Few Americans expected an easy victory. The debacle of the Vietnam War still cast a long shadow. “Yours is a society that cannot accept 10,000 dead,” Saddam told the U.S. ambassador to Kuwait a week before he invaded his neighbor. Many analysts worried that he might be right, and the Senate authorized force by only a narrow margin. The Pentagon prepared for heavy losses, shipping thousands of body bags to the region. The expectation was not another World War II. It was another Vietnam.

What followed shocked almost everyone. After five weeks of air attacks, coalition ground forces liberated Kuwait in roughly 100 hours. The Iraqi army crumbled. More than 300,000 Iraqi troops in Kuwait were defeated, captured, or forced to flee. American combat deaths totaled 147, a stunningly low figure given concerns entering the war. A major state that had seemed formidable only months earlier had been routed with astonishing ease.

The significance of the American triumph extended well beyond the battlefield, underscoring the extraordinary position of the United States. With the Soviet Union disintegrating, Washington faced no major adversary and sat at the center of the world's financial, technological, and alliance networks. It boasted advanced military capabilities that no other power could match. The United States had become something unusual in modern history: a single state without a peer competitor. Operation Desert Storm transformed abstract measures of American power into lived experience. Governments, investors, and ordinary citizens around the world now possessed a shared image of what American military dominance meant in practice.

Most wars disappear into history. A few divide history into before and after. For the post–Cold War world, the Gulf War was one of those moments. The conflict resulted in the liberation of Kuwait and then launched the age that followed, one commonly referred to as an era of U.S. unipolarity, when peerless American military power undergirded globalization, growing prosperity, and relative stability.

But that age has now come to an end. The United States no longer enjoys the sort of military advantage it possessed in 1991. Thanks to globalization, the systems necessary to conduct precision warfare are no longer the preserve of a handful of great powers: they are accessible to a range of actors who are now able to stand up to much stronger states.

Indeed, the Iran war exemplifies this turning of the wheel. Where the Gulf War demonstrated American dominance, today’s clashes around the Strait of Hormuz reveal American limitations. A new era beckons, one in which the assumptions of the post–Cold War period are turned on their heads. The United States is not capable of bending others to its will through the exercise of force at low cost. Far from guaranteeing stability and predictability, American power has become a source of volatility. Weaker powers have learned the virtues of defiance and disruption, and they possess the tools to impose huge costs on the United States and its allies and partners. The coming era will be one of more frequent crises, higher costs for protecting global commerce, and intensifying competition over the world’s strategic chokepoints. The rules of power that governed the post–Cold War era have withered away, and a more dangerous international order awaits.

Major military victories do not often create new international orders. Wars can end with altered borders but they tend to leave the larger structure of world politics intact. The 1991 Gulf War was different because it transformed the world’s expectations. The gargantuan gap between what analysts predicted before the war and how the United States won a decisive and rapid victory convinced governments, markets, and societies that a new reality had emerged.

That reality rested on four assumptions: The United States could effortlessly impose military outcomes. Washington possessed unmatched escalation dominance, the capacity to quickly and cheaply defeat major threats. American power guaranteed the flow of goods through the world’s commercial arteries. And resistance to American power was ultimately futile.

These assumptions reinforced one another. Because American military superiority appeared overwhelming, allies reduced their own defense burdens and deepened their dependence on Washington. Because American power discouraged other actors to risk confrontation and escalation, investors discounted geopolitical risk. Because maritime commerce appeared secure, corporations stretched supply chains across continents and minimized their inventories at home. Because American power appeared unrivaled and implacable, most states sought to accommodate the United States rather than resist it.

The post–Cold War order rested less on Washington’s capacity for coercion than on the strength of its credibility. States did not need to experience American military power directly. They only needed to believe in it. The United States defeated Iraq so quickly and so cheaply that future resistance appeared irrational. Only a handful of “rogue states” and actors, such as North Korea, Iran, and Somali pirates, dared to ignore what all could see. In 1990, the U.S. Air Force ambitiously called its new doctrine “Global Power, Global Reach.” The 1991 Gulf War made this a reality few could ignore.

The seeming invincibility of American power heralded by the Gulf War had immediate consequences in Europe. During the Cold War, Western European governments had maintained large militaries because the threat of the Soviet Union required them to do so. After 1991, European countries slashed defense budgets while increasingly integrating their economies. They signed the Maastricht Treaty in 1992, laying the groundwork for a shared currency and the flattening of borders among EU member states. Formerly communist........

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