The dispute over the South China Sea, one of the most complicated geopolitical issues of the 21st century, keeps heating up. China, Taiwan, Malaysia, the Philippines, Vietnam, and other regional governments are all part of the dispute – along with the United States.

Here are four key things to know about the dispute.

1. What's At Stake

The South China Sea holds immense resources, from the oil and gas located underneath the seabed to the lucrative fishing it has afforded for generations.

"It's a race to build and bolster presence," says Andrew Scobell, a senior political scientist at the RAND Corporation. "Control over the sea means greater access to fisheries and more leverage over its shipping lanes."

More than $5 trillion worth of trade passes through these waters every year, from Middle East oil bound for Asian markets to plastic lawn furniture on its way from China to your local Home Depot.

But the dispute is not just about economic assets. The sea's strategic location near half a dozen East and Southeast Asian countries provides incentives for governments to seek control of the military and civil activity around the waters.

Hence the overlapping claims.

2. Whose Waters?

Seven different states claim parts of the South China Sea – China, Brunei, Taiwan, Malaysia, Indonesia, Vietnam and the Philippines. Many of these claims overlap, spurring the race for control over the sea's islands, reefs, and rocks.

Taiwan's government in March flew journalists to Taiping Island, an all-but-invisible patch of sand in the Spratly Island formation. Taipei wants to prove the formation is "not just a rock," but an island capable of sustaining human life.

The distinction between island and rock is important. Owners of islands are entitled to an "exclusive economic zone" out to 200 nautical miles. Rocks do not receive the same designation.

With this in mind, Vietnam and the Philippines have raced to set up shop on contested rocks, coral reefs, and sandbars, turning them into islands through dredging and military fortification.

But no country has built as feverishly as China. And to U.S. Pacific Command Chief Adm. Harry Harris, the reason for China's push is clear.

"China seeks hegemony in East Asia," he said. "Simple as that."

3. China's Strategy

"In essence, China sees the sea as a big Chinese lake," said RAND's Scobell. "The precise contours of its claims are vague, but it is clear China claims the majority of the islands, reefs, and territorial waters within the infamous 'nine-dash line.'"

The nine-dash line marks a claim of sovereignty that scoops into the South China Sea from the Luzon Strait between Taiwan and the Philippines, south to Malaysia, and northeast into the waters of Vietnam. It dates from a 1947 claim by the then-Republic of China, now Taiwan.

Beijing has avoided making a formal claim of sovereignty, possibly to give itself more room to maneuver in international negotiations.

"There are dubious grounds in international law for claiming the nine-dash line," Scobell said.

If China formalizes its claims, it risks undermining a status quo that allows it to build with relative impunity and establish sovereignty over the sea's economic assets.

The Association of Southeast Asian Nations (ASEAN) has called for the enforcement of a 13-year-old Code of Conduct in the South China Sea. Beijing, however, is unlikely to get behind a multi-party deal where its influence is diminished.

"China would much rather negotiate with Southeast Asian nations on a bilateral basis than with ASEAN as a whole," says Victor Cha, director of Asia Studies at Georgetown University. "Beijing very much took a page from the U.S. playbook in this case – you're better off cutting smaller deals where you wield a lot more influence."

Focusing on smaller deals plays well with China's piecemeal approach to the South China Sea. Slow and steady construction can eventually turn a few airstrips and outposts into a vast military complex able to dominate the sea and airspace alike.

4. Despite alliances, the U.S. is hesitant to do much

Washington's fear of unintended confrontations with China plays into Beijing's grand strategy in the South China Sea, analysts say.

"China knows the United States will not go to war over atolls and coral reefs," Cha said. "These are not critical U.S. security interests."

But the United States does maintain vital alliance structures in the Western Pacific, which could pull it into direct confrontation with China.

For example, the 1979 Taiwan Relations Act could require the U.S. to intervene militarily if China invades or attacks Taiwan. Both China and Taiwan claim to be the official government of China; their claims over the South China Sea are almost identical.

The potential for deteriorating cross-strait relations puts the United States in a tough spot – it must uphold its security commitments to Taiwan while avoiding confrontation with Chinese vessels patrolling Taiwanese islands.

Beijing has taken advantage of Washington's careful balance in the South China Sea by continuing its slow and steady construction and militarization.

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