The post-Cold War era began, in the early 1990s, with soaring visions of global peace. It is ending, three decades later, with surging risks of global war. Today, Europe is experiencing its most devastating military conflict in generations. A brutal fight between Israel and Hamas is sowing violence and instability across the Middle East. East Asia, fortunately, is not at war. But it isn’t exactly peaceful, either, as China coerces its neighbors and amasses military power at a historic rate. If many Americans don’t realize how close the world is to being ravaged by fierce, interlocking conflicts, perhaps that’s because they’ve forgotten how the last global war came about.

When Americans think of global war, they typically think of World War II—or the part of the war that began with Japan’s strike on Pearl Harbor in December 1941. After that attack, and Adolf Hitler’s subsequent declaration of war against the United States, the conflict was a single, all-encompassing struggle between rival alliances on a global battlefield. But World War II began as a trio of loosely connected contests for primacy in key regions stretching from Europe to the Asia-Pacific—contests that eventually climaxed and coalesced in globally consuming ways. The history of this period reveals the darker aspects of strategic interdependence in a war-torn world. It also illustrates uncomfortable parallels to the situation Washington currently confronts.

The United States isn’t facing a formalized alliance of adversaries, as it once did during World War II. It probably won’t see a replay of a scenario in which autocratic powers conquer giant swaths of Eurasia and its littoral regions. Yet with wars in eastern Europe and the Middle East already raging, and ties between revisionist states becoming more pronounced, all it would take is a clash in the contested western Pacific to bring about another awful scenario—one in which intense, interrelated regional struggles overwhelm the international system and create a crisis of global security unlike anything since 1945. A world at risk could become a world at war. And the United States isn’t remotely ready for the challenge.

WAR AND REMEMBRANCE

American memories of World War II are indelibly marked by two unique aspects of the U.S. experience. First, the United States entered the war very late—more than two years after Hitler rocked Europe by invading Poland, and more than four years after Japan initiated the Pacific War by invading China. Second, the United States joined the fight in both theaters simultaneously. World War II was thus globalized from the moment the United States entered it; from December 1941 onward, the conflict featured one multicontinent coalition, the Grand Alliance, fighting another multicontinent coalition, the Axis, on multiple fronts. (The exception was that the Soviet Union remained at peace with Japan from 1941 until 1945.) This was a world war in its fullest, most comprehensive sense. Yet history’s most terrible conflict didn’t start that way.

World War II was the aggregation of three regional crises: Japan’s rampage in China and the Asia-Pacific; Italy’s bid for empire in Africa and the Mediterranean; and Germany’s push for hegemony in Europe and beyond. In some ways, these crises were always linked. Each was the work of an autocratic regime with a penchant for coercion and violence. Each involved a lunge for dominance in a globally significant region. Each contributed to what U.S. President Franklin Roosevelt, in 1937, called a spreading “epidemic of world lawlessness.” Even so, this wasn’t an integrated mega-conflict from the outset.

The fascist powers initially had little in common except illiberal governance and a desire to shatter the status quo. In fact, the vicious racism that pervaded fascist ideology could work against the cohesion of this group: Hitler once derided the Japanese as “lacquered half-monkeys.” And although these countries, beginning in 1936, would seal a series of overlapping security pacts, through the late 1930s they were as often rivals as allies. Hitler’s Germany and Prime Minister Benito Mussolini’s Italy worked at cross-purposes in crises over Austria in 1934 and Ethiopia in 1935. As late as 1938, Germany was supporting China in its war of survival against Japan; the next year, it signed a tacit alliance with the Soviet Union, then fighting an undeclared conflict against Tokyo in Asia. (Moscow and Tokyo later signed a non-aggression pact in April 1941, which held until 1945.) Only gradually did regional crises merge, and rival coalitions cohere, because of factors that might sound familiar today.

First, whatever their specific—and sometimes conflicting—aims, the fascist powers had a more fundamental similarity of purpose. All were seeking a dramatically transformed global order, in which “have not” powers carved out vast empires through brutal tactics—and in which brutal regimes surpassed the decadent democracies they despised. “In the battle between democracy and totalitarianism,” Japan’s foreign minister declared in 1940, “the latter . . . will without question win and will control the world.” There was a basic geopolitical and ideological solidarity among the world’s autocracies, which thrust them—and the conflicts they sowed—closer together over time.

Second, the world developed a perverse form of interdependence, as instability in one region exacerbated instability in another. By humiliating the League of Nations and showing that aggression could pay, Italy’s assault on Ethiopia in 1935 paved the way for Hitler’s remilitarization of the Rhineland in 1936. Germany then paid it forward in 1940 by crushing France, putting the United Kingdom on the brink, and creating a golden opportunity for Japanese expansion into Southeast Asia. Particular tactics also migrated from theater to theater; the use of terror from the air by Italian forces in Ethiopia, for instance, prefigured its use by German forces in Spain and Japanese forces in China. Not least, the sheer number of challenges to the existing order disoriented and debilitated its defenders: the United Kingdom had to tread carefully in dealing with Hitler in crises over Austria and Czechoslovakia in 1938 because Japan threatened its imperial holdings in Asia and its Mediterranean lifelines were vulnerable to Italy.

These two factors contributed to a third, which was that programs of extreme aggression polarized the world and divided it into rival camps. In the late 1930s, Germany and Italy banded together for mutual protection against Western democracies that might try to frustrate their respective ambitions. In 1940, Japan joined the party in hopes of deterring the United States from interfering with its expansion in Asia. Through multiple, mutually reinforcing programs of regional revisionism, the three countries declared, they would create a “new order of things” in the world.

This new Tripartite Pact didn’t ultimately deter Roosevelt, but it did convince him, as he wrote in 1941, that “the hostilities in Europe, in Africa, and in Asia are all parts of a single world conflict.” Indeed, as the Axis cohered and its aggression intensified, it gradually forced a vast array of countries into a rival alliance dedicated to frustrating those designs. When Japan attacked Pearl Harbor, and Hitler declared war on Washington, they brought the United States into conflicts in Europe and the Pacific—and turned those regional clashes into a global struggle.

PAST IS PRESENT

The parallels between this earlier era and the present are striking. Today, as in the 1930s, the international system is facing three sharp regional challenges. China is rapidly amassing military might as part of its campaign to eject the United States from the western Pacific—and, perhaps, become the world’s preeminent power. Russia’s war in Ukraine is the murderous centerpiece of its long-standing effort to reclaim primacy in eastern Europe and the former Soviet space. In the Middle East, Iran and its coterie of proxies—Hamas, Hezbollah, the Houthis, and many others—are waging a bloody struggle for regional dominance against Israel, the Gulf monarchies, and the United States. Once again, the fundamental commonalities linking the revisionist states are autocratic governance and geopolitical grievance; in this case, a desire to break a U.S.-led order that deprives them of the greatness they desire. Beijing, Moscow, and Tehran are the new “have not” powers, struggling against the “haves”: Washington and its allies.

Two of these challenges have already turned hot. The war in Ukraine is also a vicious proxy contest between Russia and the West; Russian President Vladimir Putin is buckling down for a long, grinding struggle that could last for years. Hamas’s attack on Israel last October—enabled, if perhaps not explicitly blessed, by Tehran—triggered an intense conflict that is creating violent spillover across that vital region. Iran, meanwhile, is creeping toward nuclear weapons, which could turbocharge its regional revisionism by indemnifying its regime against an Israeli or U.S. response. In the western Pacific and mainland Asia, China is still relying mostly on coercion short of war. But as the military balance shifts in sensitive spots such as the Taiwan Strait or the South China Sea, Beijing will have better options—and perhaps a bigger appetite—for aggression.

As in the 1930s, the revisionist powers don’t always see eye-to-eye. Russia and China both seek preeminence in central Asia. They are also pushing into the Middle East, in ways that sometimes cut across Iran’s interests there. If the revisionists do eventually push their common enemy, the United States, out of Eurasia, they might end up fighting among themselves over the spoils—just as the Axis powers, had they somehow defeated their rivals, surely would have then turned on one another. Yet for now, the ties between revisionist powers are flourishing and Eurasia’s regional conflicts are becoming more tightly interlinked.

Russia and China are drawing closer through their “no limits” strategic partnership, which features arms sales, deepening defense-technological cooperation, and displays of geopolitical solidarity such as military exercises in global hot spots. And just as the Molotov-Ribbentrop pact of 1939 once allowed Germany and the Soviet Union to rampage through eastern Europe without risking conflict with each other, the Sino-Russian partnership has pacified what was once the world’s most militarized border and enabled both countries to focus on their contests with Washington and its friends. More recently, the war in Ukraine has also enhanced other Eurasian relationships—between Russia and Iran, and Russia and North Korea—while intensifying and interweaving the challenges the respective revisionists pose.

Drones, artillery ammunition, and ballistic missiles provided by Tehran and Pyongyang—along with economic succor provided by Beijing—have sustained Moscow in its conflict against Kyiv and its Western backers. In exchange, Moscow appears to be transferring more sensitive military technology and know-how: selling advanced aircraft to Iran, reportedly offering aid to North Korea’s advanced weapons programs, perhaps even helping China build its next-generation attack submarine. Other regional tussles are revealing similar dynamics. In the Middle East, Hamas is fighting Israel with Chinese, Russian, Iranian, and North Korean weapons that it has been accumulating for years. Since October 7, Putin has declared that conflicts in Ukraine and the Middle East are part of a single, larger struggle that “will decide the fate of Russia, and of the entire world.” And in another echo of the past, tensions across Eurasia’s key theaters stretch U.S. resources thin by confronting the superpower with multiple dilemmas simultaneously. The revisionist powers aid each other simply by doing their own things.

One crucial difference between the 1930s and today is the scale of the revisionism. As bad as Putin and Iranian Ayatollah Ali Khamenei are, they haven’t devoured huge chunks of crucial regions. Another crucial difference is that East Asia still enjoys a tenuous peace. But with U.S. officials warning that China could become more belligerent as its capabilities mature—perhaps as soon as the second half of this decade—it is worth considering what would happen if that region erupted.

Such a conflict would be catastrophic in multiple respects. Chinese aggression against Taiwan could well trigger a war with the United States, pitting the world’s two most powerful militaries—and their two nuclear arsenals—against each other. It would wrench global commerce in ways that make the dislocations provoked by the wars in Ukraine and Gaza look trivial. It would further polarize global politics as the United States seeks to rally the democratic world against Chinese aggression—pushing Beijing into a tighter embrace with Russia and other autocratic powers.

Most critically, if combined with ongoing conflicts elsewhere, a war in East Asia could create a situation unlike anything since the 1940s, in which all three key regions of Eurasia are ablaze with large-scale violence at once. This might not become a single, all-encompassing world war. But it would make for a world plagued by war as the United States and other defenders of the existing order confronted multiple, interlocking conflicts spanning some of the most important strategic terrain on Earth.

GATHERING STORMS

There are lots of reasons that this scenario might not happen. East Asia could remain at peace, because the United States and China have immense incentives to avoid a horrific war. The fighting in Ukraine and the Middle East could subside. But thinking through the nightmare scenario is still worthwhile, since the world could be as little as one mishandled crisis away from pervasive Eurasian conflict—and because the United States is so unprepared for this eventuality.

Right now, the United States is straining to support Israel and Ukraine simultaneously. The demands of these two wars—fights in which Washington is not yet a principal combatant—are stretching U.S. capabilities in areas such as artillery and missile defense. Deployments to the waters around the Middle East, meant to deter Iran and keep critical sea lanes open, are taxing the resources of the U.S. Navy. Strikes against Houthi targets in Yemen are consuming assets, such as Tomahawk missiles, that would be at a premium in a U.S.-Chinese conflict. These are all symptoms of a bigger problem: the shrinking ability and capacities of the U.S. military relative to its numerous, interrelated challenges.

During the 2010s, the Pentagon gradually shifted away from a military strategy meant to defeat two rogue-state adversaries at the same time, opting instead for a one-war strategy aimed at defeating a single great-power rival, China, in a high-intensity fight. In one sense, this was a sensible response to the extreme demands such a conflict would entail. But it has also left the Pentagon ill equipped for a world in which a combination of hostile great powers and serious regional threats are menacing multiple theaters at once. It has also, perhaps, emboldened more aggressive U.S. adversaries, such as Russia and Iran, which surely realize that an overstretched superpower—with a military desperate to focus on China—has limited ability to respond to other probes.

Of course, the United States wasn’t ready for global war in 1941, but it eventually prevailed through a world-beating mobilization of military and industrial might. President Joe Biden evoked that achievement late last year, saying the United States must again be the “arsenal of democracy.” His administration has invested in expanding the production of artillery ammunition, long-range missiles, and other important weapons. But the harsh reality is that the defense industrial base that won World War II and then the Cold War no longer exists, thanks to persistent underinvestment and the broader decline of U.S. manufacturing. Shortages and bottlenecks are pervasive; the Pentagon recently acknowledged “material gaps” in its ability to “rapidly scale production” in a crisis. Many allies have even weaker defense industrial bases.

Thus, the United States would have great difficulty mobilizing for a multitheater war, or even mobilizing for protracted conflict in a single region while keeping allies supplied in others. It might struggle to generate the vast magazines of munitions needed for great-power conflict or to replace ships, planes, and submarines lost in the fighting. It would surely be hard-pressed to keep pace with its most potent rival in a potential war in the western Pacific; as a Pentagon report puts it, China is now “the global industrial powerhouse in many areas—from shipbuilding to critical minerals to microelectronics,” which could give it a crucial mobilization advantage in a contest with the United States. If war does engulf multiple theaters of Eurasia, Washington and its allies might not win.

It isn’t helpful to pretend that there is an obvious, near-term solution to these problems. Focusing U.S. military power and strategic attention overwhelmingly on Asia, as some analysts advocate, would take a toll on American global leadership in any circumstances. At a time when the Middle East and Europe are already in such profound turmoil, it could be tantamount to superpower suicide. But although dramatically ramping up military spending to drive down global risk is strategically essential, it seems politically inexpedient, at least until the United States suffers a more jarring geopolitical shock. In any case, it would take time—time Washington and its friends might not have—for even sizable increases in defense outlays to have a tangible military effect. The Biden administration’s approach seems to involve muddling through in Ukraine and the Middle East, making only marginal, selective increases in military spending, and betting the house that China doesn’t become more bellicose—a policy that could work well enough, but could also fail disastrously.

The international scene has darkened dramatically in recent years. In 2021, the Biden administration could envision a “stable and predictable” relationship with Russia—until that country invaded Ukraine in 2022. In 2023, U.S. officials deemed the Middle East quieter than at any time this century—just before a devastating, regionally destabilizing conflict broke out. U.S.-Chinese tensions aren’t particularly febrile at the moment, but sharpening rivalry and a shifting military balance make for a dangerous mix. Great catastrophes often seem unthinkable until they happen. As the strategic environment deteriorates, it’s time to recognize how eminently thinkable global conflict has become.