BEIJING — The United States has a whole host of security headaches to worry about right now. In the Middle East, defeating ISIS is a top priority, while horrific terror attacks in Brussels and Paris offered a stark reminder of the continued threat posed by radical terrorism. In Europe, Russia's Vladimir Putin seems intent on resurrecting the clout wielded by the former Soviet Union.

That's why it may seem puzzling that the U.S. has become embroiled in yet another potential flash zone -- the South China Sea. In that waterway, located off the southeast coast of Asia, Washington is tied up in what appears to be a series of arcane territorial disputes over islands that are, in many cases, no more than uninhabited rocks and reefs. And in the process, the U.S. has become locked in an increasingly tense standoff with a rising China .

Yes, the details may sound pointless, but the point behind them is critical. The South China Sea has become the premier test of America's ability to preserve its primary security role in Asia, and prove to its allies in the region that the U.S. can contend with the challenge posed by an assertive Communist China gaining in wealth and power. From Washington’s perspective, allowing China to bully its way to dominance in the sea would undermine the norms of international relations the U.S. has instituted since the end of World War II.

Though the conflicts in the Middle East may seem more pressing, Gregory Poling, director of the Asia Maritime Transparency Initiative at the Center for Strategic & International Studies in Washington, argues that an expanding Asia is of greater importance to America’s future. “The Asia-Pacific is where U.S. interests ultimately lie,” Poling says. “We cannot afford to be a nation with a short attention span.”

With so much on the line, the tension between the U.S. and China has recently ratcheted upwards. U.S. Secretary of Defense Ash Carter warned during a forum in Singapore in early June that "China has taken some expansive and unprecedented actions" in the sea. If continued, he said, "China could end up erecting a Great Wall of self-isolation." Undeterred, Sun Jianguo, a Chinese admiral, shot back that "we do not make trouble, but we have no fear of trouble,"

The contest is not just one of words. In May, the Pentagon said Chinese fighter jets flew within 50 feet of a U.S. surveillance plane on a routine mission over the South China Sea in an incident U.S. officials considered potentially unsafe – just the sort of incident that can lead to accidents, and conflicts. (China’s foreign ministry, in response, said the Pentagon’s claims were “not true” and called on the U.S. to end such operations.)

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There is no ready solution to the growing tensions. Beijing claims nearly all of the South China Sea as its own – even equating its military deployments there with the U.S. defense of Hawaii. To strengthen its claims, China has literally been building up isolated reefs into full-fledged islands , complete with what appear to be military installations.

However, China's neighbors don't recognize its claims in the South China Sea. Vietnam , Malaysia , the Philippines , Taiwan and Brunei all forward their own territorial rights to parts of the sea. These countries see China's actions as an attempt to unilaterally assert its control. The U.S., meanwhile, has stepped in to support its allies, as well as what it considers freedom of navigation, and has repeatedly sent warships and planes into the disputed waters to uphold that right. Carter, in Singapore , reiterated that the U.S. "will continue to fly, sail, and operate wherever international law allows, so that everyone in the region can do the same."

The U.S. position is that the competing claims and counterclaims should be sorted out peacefully through negotiation. China, though, doesn't seem interested. Beijing has already said it will reject the verdict made by an international tribunal in The Hague in a case submitted by the Philippines contesting China's assertions.

All parties have reason to dig in. The South China Sea is a major thoroughfare of commerce – some $5.3 trillion in trade passes through each year – and the U.S. and its allies fear China might try to impede this critical shipping. There is also speculation that there are significant resources of natural gas and oil still untapped in the sea , which could be exploited by whichever nation can assert its claims.

China's position goes well beyond the practical, however. President Xi Jinping has charted a more assertive foreign policy to paint himself as a defender of Chinese national interests, and his stand in the South China Sea is a central part of that strategy. The Chinese media releases a nearly daily drumbeat of stories accusing the U.S. of "meddling" in Chinese affairs, paired with strident statements defending Beijing's claims. With Xi's public image linked so directly to the South China Sea, compromise will be politically difficult for Beijing.

As a result, there are worries that China will take even further aggressive steps to solidify its position, such as declaring an air-defense zone over the South China Sea. U.S. Secretary of State John Kerry has already said that Washington would consider such a move "a provocative and destabilizing act."

The U.S., too, has little incentive to back down. More countries in the region are looking to Washington for support against Chinese encroachment. During President Barack Obama's May visit to Vietnam, he lifted a long-standing ban on the sale of weaponry to the country, a clear sign of how the two one-time adversaries are growing closer together.