China and Japan, the world's second and third largest economies, do not get along. Increasingly noisy nationalist movements in both countries seem to consider the other country their ancient enemy, with citizens leading sometimes violent anti-Japanese or anti-Chinese protests and national leaders, including the heads of state, promoting confrontation over diplomacy.

The two most recent conflict points are a string of tiny, disputed islands, called the Senkaku in Japan and Diaoyu in China, to which both countries have sent increasingly belligerent naval patrols, and Japanese Prime Minister Shinzo Abe's hints that he might partially retract Japan's official apologies for its World War II-era abuses in Asia.

These conflicts can often look like just the most recent manifestations of an ancient and sometimes vicious rivalry. And this is often the view in those countries themselves. As Japanese Deputy Prime Minister Taro Aso said during a recent visit to India, "For the past 1,500 years and more, there has never been a history when our relations with China went extremely smoothly."

In this telling, the ancient, ingrained tensions are being worsened by present-day factors: China's rise, Japan's decline, the unaddressed legacy of World War II. But what if it's the other way around? What if its those contemporary (and temporary) issues that are driving the war-of-words, with past conflict little more than an excuse?

That's what Ian Buruma, a highly respected historian who focuses on Asia (and who wrote "Inventing Japan: 1853-1964," a great book about modern Japan), argues in an essay for the Wall Street Journal. "On the surface, the dispute is about history," Buruma writes. "In fact, it is more about politics, domestic and international, revealing the tangled relations in a region where history is frequently manipulated for political ends."

It turns out that even China's communist-era founder, Mao Zedong, had pretty smooth relations with Japan. The conflict, in other words, is much, much more recent than you might think. Here's Buruma with a surprising story from Mao's era, when things seemed downright jovial:

When Prime Minister Kakuei Tanaka visited Beijing in 1972 to restore Japan's relations with China, a country that had been devastated by Japanese military aggression in the 1930s and '40s, his host Mao Zedong allowed himself a moment of levity. Responding to Tanaka's apology for what Japan had done during the war, Mao answered that there was absolutely no need to apologize. After all, he said, without the Japanese invasion, the Communist revolution would never have succeeded.
Secure in his nationalist credentials, as the leader who unified China, Mao could afford this little joke, which also happened to be the truth. Such a remark would be unimaginable for any of the technocrats who rule China today. Maoism can no longer justify the Communist Party's monopoly on power, since few Chinese believe in any kind of Communism. Nationalism is now the dominant ideology, and the rulers have to prove their mettle, especially toward Japan. This need is particularly acute when a new leader takes power. The latest party boss, Xi Jinping, needs to show people, not least the military brass, that he is in charge.

In other words, because Chinese isn't really Maoist or Marxist anymore, the country had to find a new ideology, a new way to legitimate the Communist Party's rule. That ideology is nationalism, but nationalism requires an "other," a foreign country to galvanize patriotism and against which to define national identity.

And the United States has played a role in all of this, using its post-war influence in Japan (we still have tens of thousands of troops there, and the U.S.-backed pacifist constitution leaves the country conveniently reliant on U.S. support) to "contain" China. Buruma writes, "Even when Japanese businessmen pressed for closer relations with China in 1970, the Japanese prime minister, Eisaku Sato, staved them off out of deference to the U.S. policy of containing China."

And Japan has still not fully recovered its own national identity, which was once sternly nationalist but was outright destroyed when the country lost World War II. The country's struggle to reinvent itself, ongoing for 60 years now, includes a major dilemma about whether or not Japan gets to be a real world power again.

This internal tension between "the need to act like a major power while still being deferential to American interests," as Buruma puts it, has sometimes led the country's leaders to embrace nationalism as a way to compensate for the embarrassing reliance on the United States. Buruma argues that the only way to return stability to East Asia is for the United States to withdraw from Japan and allow the country greater independence.

Maybe he's right, but if the United States really leaves Japan on its own at a time when the country's power is declining and China's is rising, that will force Tokyo to make a very difficult choice:

Japan could rearm, maybe even develop nuclear weapons so that it will be strong enough to balance against China. Members of the foreign policy "realist" school warn that this could lead to a potentially dangerous China-Japan arms race.

Or Japan could choose to "bandwagon" with China rather than competing with it, thus turning it back against the United States. This would potentially transform the balance of power in East Asia, making China rather the United States the dominant power, something that could have enormous knock-on effects in the region, for example on the Korean peninsula, with South Korea suddenly isolated among its neighbors.

That's a worst-case hypothetical, but it's exactly the sort of scenario that the Obama administration is seeking to avoid with its "pivot to Asia."