Chinese foreign policy under Xi Jinping rests on certain basic assumptions: that in a just world, China should be hegemonic in East Asia, the center of a system in which the other regional powers pay their respect and take direction from China, as was the case for two millennia prior to the 19th century; that regions once considered by Beijing to have been part of China should be “reunified” with it; and that a revived China should have at least an equal say in setting the norms and rules of international life. These goals are achievable, Mr. Xi asserts, because the world is undergoing “great changes unseen in a century,” namely, the “great rejuvenation” of Chinese power and the decline of American power. “Time and momentum are on our side,” according to Mr. Xi.

There is no denying that China has acquired substantial global power and influence in recent decades. Even if this is “peak China,” as some suggest, it is already East Asia’s economic hegemon and, were it not for the U.S., would likely become the region’s political and military hegemon as well (though perhaps not without a conflict with Japan). Left to itself, a modernizing China could one day dominate its neighbors much as a unified, modernizing Germany once dominated Europe and a modernizing Japan once dominated China and the rest of East Asia. Those powers also believed that “time and momentum” were on their side, and in many respects they were right.

Yet those examples should give Chinese leaders pause, for both Japan and Germany, while accomplishing amazing feats of rapid expansion for brief periods of time, ultimately failed in their ambitions for regional hegemony. They underestimated both the actual and potential power of the U.S. They failed to understand that the emergence of the U.S. as a great power at the beginning of the 20th century had so transformed international circumstances that longstanding ambitions of regional hegemony were no longer achievable. At this moment of high tension over Taiwan and the Chinese spy balloon detected this week over the U.S., Xi Jinping runs the risk of making the same historic mistake.

The world entered a new phase when the U.S. emerged as a great power at the beginning of the 20th century. As Theodore Roosevelt observed in 1900, the U.S., due to its “strength and geographical situation,” had become “more and more the balance of power of the whole globe.” This was no metaphor. As Germany discovered in World War I, the U.S. could determine the outcome of any major regional conflict by bringing its vast wealth, population and productive capacity to bear on one side or the other. Although the Germans correctly calculated their military and economic superiority over their neighbors, the additional millions of fresh American troops and billions of American dollars’ worth of supplies quickly made their situation untenable. As one top German general put it, “We cannot fight the whole world.”

In World War II, Germany and Japan may have correctly judged their chances of success against their regional opponents. By early 1942, well over half the planet’s productive capacity was under the control of the Axis powers—Germany, Japan and Italy. Yet even then the entry of the U.S. into the war marked the beginning of the end for all three powers and their regimes. As an exasperated Hitler observed, the Americans and British together had “the world at their disposal.” In addition to America’s size, wealth and productive capacity, it enjoyed something close to invulnerability from foreign invasion. Hitler once remarked that Germany had as much a chance of conquering America as America had of conquering the moon, and he admitted soon after the U.S. entered the war that he had no idea how to defeat it.

Victims of aggression, especially those with liberal regimes, came to expect sympathy and eventual support from America. The problem was not just America’s power and relative invulnerability. Prior to the emergence of the U.S., regional hegemons could generally count on their weaker neighbors to accommodate their rising power. But the arrival of the U.S. as a power with global influence at the start of the 20th century changed the equation. Would-be victims of aggression, especially those with liberal regimes, came to expect sympathy and eventual support from liberal America. As Winston Churchill put it after Dunkirk, the British would fight on until “in God’s own time, the New World, with all its power and might, steps forth to the rescue and the liberation of the old.”

The expectation of eventual American support proved a critical factor in Europe before and during World War II. As Hitler remarked ruefully to his generals in January 1941, hope for America’s help “keeps Britain going.” In 1934, Tokyo blocked any further Western assistance to the Chinese, correctly believing that it discouraged the Chinese from accepting Japanese rule. Let Asia be for the Asians, was the Japanese slogan, which in practice meant letting Japan manage relations with its neighbors without American interference. Hitler, too, promised to leave “America for the Americans” if the U.S. would just leave “Europe for the Europeans,” which was to say, for Germany.

The critical role the U.S. played in the decision-making of others was best demonstrated over the course of the 1920s and ‘30s. For the first decade and a half after the end of World War I, as the U.S. stepped away from direct involvement in Europe, the European powers did indeed try to settle their own problems in the only way left to them—by accommodating the rising power and growing ambitions of Germany. America’s policy of deliberate disinterest—codified in the neutrality laws of the mid- and late-1930s—played a critical part in convincing Britain’s Neville Chamberlain to pursue appeasement. The agreement at Munich to give parts of Czechoslovakia to Germany was the result of a domino effect that began with the U.S.: The Czechs, though prepared to fight the Germans, could not do so without the support of Britain and France, but the British and French would not offer their support if they could not count on the U.S. to back them up.

Appeasement ended after 1938 not just because Hitler reneged and took the rest of Czechoslovakia but because it became clear to everyone that the Americans, led by President Franklin D. Roosevelt, were finally changing their minds about the importance of Europe. Even this flicker of hope was enough to make them resist. Hitler blamed the U.S. both for Poland’s rejection of his territorial demands in 1939 and for Britain and France’s decision to declare war after he invaded Poland that year.

In both world wars, the aggressors believed that the U.S. would not try to stop them.
America’s unpredictability itself posed a problem for would-be aggressors, for in each crisis the aspiring hegemonic powers badly misjudged both American capabilities and, perhaps more importantly, American intentions. In both world wars, the aggressors believed that the U.S. would not try to stop them and that, even if it did try, it lacked the wherewithal to make a difference in time.

Such miscalculations were understandable. The American military in both 1917 and after 1939 was not remotely prepared for industrial warfare on a global scale. In 1917 the Americans could not deploy more than 25,000 troops abroad for any length of time and lacked a navy capable of operating with effect in both the Pacific and the Atlantic theaters at the same time. In 1939 the Luftwaffe had 8,000 new aircraft; the U.S. Army Air Force had 1,700 mostly outdated planes. The German army had 2,000 new tanks; the U.S. had 325, many of World War I vintage. Meanwhile, the Imperial Japanese Navy had more and better warships than anything the Americans could put in Pacific waters, especially once the war in the Atlantic heated up.

Nor did the U.S. in 1939 possess the industrial plant required to boost weapons production quickly. Arms manufacturers, hounded by congressional investigations and starved of government contracts, had shut down production lines. Any significant buildup would require retooling factories and a transformation of the national economy that would take at least two years.

It was not just that the Americans were physically unprepared for war. They also insisted they would not, in fact, go to war. The neutrality legislation that barred the U.S. from even embargoing an aggressor persisted well into 1939. As late as 1941, Roosevelt was still promising not to send American soldiers overseas. It was clear to foreign observers like the Nazi leader Joseph Goebbels that, while Roosevelt might be prepared for war, the American public still wanted peace. “What is America but beauty queens, millionaires, stupid records and Hollywood?” Hitler remarked, while the great Japanese naval strategist, Admiral Isoroku Yamamoto, regarded the American people as “self-indulgent weaklings.”

Neither could imagine that the U.S. of 1939 would become the U.S. of 1942, producing weapons and materiel at a rate that defied all past experience. Between the summer of 1940 and the summer of 1945, American shipyards produced 141 aircraft carriers, eight battleships, 807 cruisers, destroyers, and destroyer escorts, and 203 submarines. American auto manufacturers and other industries converted their assembly lines to produce 88,410 tanks and self-propelled guns, 257,000 artillery pieces, 2.4 million trucks, 2.6 million machine guns and 41 billion rounds of ammunition. The budding American aviation industry eventually produced 170 aircraft per day for a total of 324,750 over the course of the war.

And who could have anticipated the furious blood lust that seized Americans after the attack on Pearl Harbor? Walter Lippmann once observed that Americans were “too pacifist in time of peace and too bellicose in time of war.” The racially charged hatred for the “Japs,” compounded by the “infamy” of the attack on Pearl Harbor, turned a generally pacifist America into a bloody-minded America. The would-be hegemons of Europe and Asia, looking at the U.S. in peacetime, could not imagine the powerful fury of which Americans were capable in wartime.

Chinese leaders today may be making the same error as past aspiring hegemons. And China, for all its growing might, starts from a less formidable position. At their peak in 1941, the Axis powers had a combined GDP larger than that of the U.S. and only a little smaller than the combined GDP of the U.S. and Britain. Today the U.S. and its allies and partners (which includes most of Europe, Japan, India, South Korea, Australia and others) produce over 50% of the world’s wealth, while China and Russia together produce a little over 20%.

The Chinese military, though large and growing, also remains untested by battle. On paper Vladimir Putin’s military looked formidable—more formidable than China’s—yet its performance has not matched its reputation. Despite billions of rubles spent on modernization, Russian technology still lags behind that of the U.S. and its allies. Nor have Russia’s nuclear weapons been of any real use in this conflict, except as a bluff. One of the great myths today is that nuclear weapons have changed all military calculations, but as the conflict in Ukraine has demonstrated, conventional war involving nuclear powers is still very possible.

China has begun its drive for regional hegemony from a much weaker starting point than past would-be hegemons. China has also begun its drive for regional hegemony from a much weaker starting point than past would-be hegemons. By the time the U.S. began to rouse itself to deal with the German challenge in World War I or with the aggressions of Germany and Japan in World War II, those great powers had already acquired both military and economic hegemony in their respective regions. Even the Soviet Union started the Cold War with hegemony over half of Europe, though in the end it could not preserve it.

China, on the other hand, does not even control all the territory in the region it regards as its own: notably, Taiwan and some islands in the East and South China Seas. It is surrounded by powerful neighbors—an India that is about to surpass China in population; a Japan that has the third largest economy in the world and could become a powerful nuclear state overnight if it chose; a South Korea that wields substantial economic and military power; and, of course, Australia. All of these countries are fearful of China’s rising power and are either allied to the U.S. or look to it to help defend themselves.

Mr. Putin, facing similar obstacles in Europe, has discovered the resilience of the American-led system and his neighbors’ willingness to resist superior Russian power when protected by it. Would the people of Ukraine, for all their courage and heroism, still be fighting Russia today without the support of the U.S. and its allies? Or would they have had to accept their fate as the neighbor of a powerful, aspiring hegemon, as the Czechs did in 1938? Who knows how well the Czechs might have fared against an untested German military had they been given the minimal support they needed? And who knows what might have become of Hitler if he, like Mr. Putin, had failed to achieve a rapid success?

Beijing faces a parallel problem in Taiwan. For most of the past three decades governments in Beijing have hoped that the people of Taiwan would gradually yield and agree to unification with the mainland. Instead, the Taiwanese have been able to defy Chinese pressure because of the support and commitments they receive from the U.S. The Chinese are bitter about this. They believe that the “One China” policy, dating from the Nixon administration, was supposed to reduce American support for Taiwan to the point where the Taiwanese would feel they had to accept Beijing’s offer of union. Things have not turned out that way. Nazi Germany defeated France, the strongest land power in Europe at the time; China has not been able to compel a small, isolated island less than one-fiftieth its size to knuckle under.

That the Germans and Japanese achieved more, and by force, does not mean they were more inherently aggressive than the Chinese might be, or than Mr. Putin has proven himself to be. They found themselves in a temporarily permissive environment when the U.S. turned inward after World War I. China’s environment has not been as accommodating because of the strength of the American-led liberal world.

Even if the Chinese did succeed in forcing Taiwan to “reunite,” either by military assault or naval blockade, would China then be in a position to exercise hegemony across East Asia? Or might that be the beginning of the end for this Chinese regime? The attack on Pearl Harbor and the subsequent destruction of American forces in the Philippines and the western Pacific were astonishing victories over the U.S., but they were also the beginning of the end for Imperial Japan. Beijing may well be able to take Taiwan, and the U.S., typically slow to prepare and respond, may not be able to prevent it. But what then?

Perhaps Mr. Xi believes that the U.S., Japan and the other powers in the region will simply adjust to the new reality. Many Americans may now think the same. There would certainly be voices in the U.S. calling for restraint. But while an attack on Taiwan would not have the same effect on Americans as the attack on Pearl Harbor, the U.S. is already very anxious about the threat of China, even when an attack on Taiwan is only prospective. It would be foolish for the Chinese to assume that such an attack would not prompt the American public to support a far more aggressive approach.

Whether the ensuing conflict is hot or cold, China would have to expect to face the full weight of the American-led liberal world order. Japan, which has already modified its pacifist constitution to allow greater military cooperation with the U.S., would likely militarize further and might even start producing nuclear weapons. India would become more concerned about China, as would all of China’s neighbors other than Russia. Even Europe is likely to view a Chinese act of aggression as yet another threat to the democratic order they are defending in Ukraine. And all will look to the U.S.

Xi may believe American power has declined dramatically, but as Putin has discovered, the contrary is true. Mr. Xi may believe American power has declined dramatically, but as Mr. Putin has discovered, the contrary is true. The ability of the American-led order to defend itself is far greater than it was in the first half of the 20th century. In 1917 and 1939, the U.S. had no overseas allies; today it has more than 50 allies and strategic partners across the globe. Prior to 1945, the U.S. had no significant overseas military presence outside the Western Hemisphere; now it has the world’s only true blue-water navy and military bases throughout the world. In the 1930s the American peacetime military was incapable of taking on other great powers; now it has a large, highly equipped and battle-tested force superior to all other militaries. And it exercises, with its rich allies, a remarkable degree of control over the global economy, with sanctions and other financial weapons that did not exist until the last three decades—as Mr. Putin has also discovered.

Is the U.S. still able to outproduce an adversary as it did in the two world wars and during the Cold War with the Soviet Union? We don’t know what a more fully mobilized 21st-century America would look like, but there is reason to think it would be formidable. This year the U.S. will spend less than 4% of its GDP on defense. That is a peacetime military budget and a comparatively low one. In Dwight Eisenhower’s last budget in 1960, the U.S. spent 9% of GDP on defense; in the Reagan years it spent just under 7%. If the U.S. spent 7% of GDP on the military today, it would amount to annual defense spending of almost $1.6 trillion, compared with the slightly over $800 billion it currently spends.

As for the technological competition, the Chinese have certainly kept up with and perhaps even rivaled the U.S. in some areas of weapons development. But would a U.S. fully geared for confrontation and possible war not be able to match China? Today, the technological superiority of American weaponry on the battlefield is evident in Ukraine. It’s possible that the Chinese could surpass the U.S. in innovation and development in an all-out, head-to-head competition, but it seems unlikely.

Are Americans as a people up to a major confrontation with another great power, whether in immediate conflict or a protracted Cold War-like struggle? It would be dangerous for a potential adversary to assume they are not. Whatever condition the American political system may be in, it is not appreciably worse than it was during the 1930s. That, too, was a deeply polarized America, including on the question of whether to intervene in the world’s conflicts. But once the U.S. found itself at war, dissent all but disappeared. If ever there could be a cure for American political polarization, a conflict with China would be it.

Can it possibly be worth it for Xi Jinping to bring on such a confrontation? Consider Mr. Putin’s attempt to conquer Ukraine. Even if Russia were to prevail—which looks increasingly unlikely—Ukraine’s neighbors would arm themselves to the teeth, the U.S. would increase its forward presence, and a new iron curtain would fall along the western borders of Ukraine. Mr. Putin’s overall objective of regaining Russian hegemony in eastern and central Europe would still be far off and likely unreachable. The U.S.-led liberal world order would still be intact and capable of blocking further Russian advances. Mr. Putin has made a very expensive investment for what in the best of circumstances must be a relatively small payout.

A Chinese takeover of Taiwan would pose the same problems. Beijing might achieve a significant strategic victory, but it would come at the price of alarming the whole world, pushing American allies into a closer embrace with Washington and frightening the American public into an all-out effort to contain and weaken China.

China’s fundamental problem, after all, is not Taiwan’s continuing de facto independence. It is the unfavorable configuration of power in the world, of which Taiwan’s defiance is only a symptom. The Chinese will likely always chafe at the liberal global hegemony that American power sustains. They will be uncomfortable relying for the security of their shipping on the goodwill of the U.S. Navy. They will be unhappy having their historic ambitions frustrated. China is the latest “have not” great power. Like Germany and Japan in the years leading up to World War II, it wants vast wealth and power, a large sphere of influence, control of the seas and a seat at the head table setting the rules of international affairs.

But what Xi Jinping’s China wants and what it can have are two different things. China is succumbing to a common malady of rising powers—an inability to be satisfied with “good enough.” The unification of Germany in 1871 was analogous to China’s recovery and success during the reforms initiated by Deng Xiaoping. The German-speaking population spread across central Europe had been weak and divided among its many small states and principalities. For Otto von Bismarck and his generation, unification was an immense, historic achievement. The Germany they created was big, rich and relatively secure—more so than at any time in the history of the German-speaking people.

Under Bismarck, Germany was a satisfied power, likely to become the hegemon of Europe simply by being the continent’s biggest economy and most populous nation. Indeed, he feared that any further German expansion or signs of ambition would lead the other European powers to gang up against it. His strategy was to balance Germany’s competitors against one another, and he was content to let Britain rule the seas and to preserve a rough balance of power in Europe with Russia and France.

The next generation of German leaders had greater ambitions, however, commensurate with their greater power. And they feared that they would be prevented from their fair share of global influence by Britain, France and Russia. Fear of being contained and denied drove Germany to precisely the end it most feared. As the historian Michael Geyer describes it, “a catastrophic nationalism” led Germans into a “real-life disaster in order to avoid mythical catastrophe.”

Japan pursued much the same tragic course. The Japanese had accomplished amazing feats by the end of the 19th century. From a position of near complete isolation, Japan emerged after the Meiji revolution in the late 19th century as the strongest power in East Asia, defeating China in 1895 and Russia a decade later. The old oligarchs of the day warned that it would be dangerous to seek more. As the respected Japanese statesman Ito Hirobumi put it in the late 1880s, “The high tree encounters strong wind.”

But younger generations of Japanese leaders were not satisfied. The Japan that emerged from World War I was stronger than ever but uncomfortably dependent on the two Anglo-Saxon powers. Many Japanese believed that their country could not keep up in the competition, win the respect it deserved and acquire the land it needed to expand unless it became an empire. Japan’s ambitions were not unreasonable for a rising power; it just turned out that those ambitions could not be accomplished without conflict with the U.S.

Modern Chinese thinking is not so different. China’s leadership sees further growth, power and expansion as necessary to its survival. They believe that the U.S. and other powers seeking to constrain China are bent on its destruction—or, more specifically, on the destruction of the Chinese Communist Party. The goal of the U.S. and its allies, Mr. Xi told a party conference early in his tenure, is “to vie with us for the battlefields of people’s hearts and for the masses, and in the end to overthrow the leadership of the CCP and China’s socialist system.”

Ideology is now also a major obstacle to China’s further “unification.” China’s crackdown on democratic institutions and forces in Hong Kong has greatly increased Taiwan’s hostility to the idea of One China, just as U.S. support encourages the Taiwanese to resist Beijing’s pressures. The two together are a disaster for Chinese ambitions.

Can Xi Jinping reconcile himself to these limits, to a world that will continue to be defined by the liberal hegemony of the U.S.?

The Japanese faced just this dilemma in 1941. By that point, leading Japanese military officials believed ultimate victory against the U.S. was unlikely. Yet the option of backing down and accepting “Little Japan” was too humiliating. It meant giving up the dream of a new Japanese-led Asian order. For Prime Minister Hideki Tojo, as for other Japanese leaders in 1940 and 1941, war was more honorable than accepting an American-imposed peace, even a losing war.

As Tojo put it, “Occasionally, one must conjure up enough courage, close one’s eyes and”—in the Japanese expression for taking the plunge—“jump off the platform of the Kiyomizu [temple].” Xi Jinping, too, may decide to take the leap. If so, he is likely to join Vladimir Putin, the Soviets, and the Axis leaders of World War II in bringing a tragedy upon his people and the world.