The US and China just had a revealing diplomatic row over military flights in the South China Sea

The US is turning into a player in the South China sea, but not in the way that Washington might like.

As the Wall Street Journal reported on December 18th, China submitted a formal diplomatic complaint to the US embassy in Beijing over a US B-52 flight within 2 nautical miles of the Cuarteron Reef, located in the South China Sea's disputed Sprately Islands.

The complaint itself reveals a hazardous geopolitical fault-line between China and the US: China complained about the flight on the basis that US warplanes had violated the airspace of an artificial island that China constructed in order to secure its claim to a disputed area.

But the US doesn't recognize China's claims of territoriality in the areas surrounding its artificial islands - a policy emphasized through a US Navy "freedom of navigation" exercise in the area in November. The US also flew a B-52 over an artificial island in the South China Sea on November 12th.

According to the WSJ report, China considered the US overflights to be "serious military provocations," infringements on Chinese territory and sovereignty that Beijing believed to be unacceptable. Yet the US rejects the underling premise of these claims, disputing the premise that the islands represent Chinese territory.

This isn't the only recent potential cause of trouble in the South China Sea. China plans on conducting military exercises in the South China Sea later in December which will include "submarines and fighter jets simulating cruise missile strikes on ships," according to Reuters.

Reuters also reported on December 18th that Japan, which has a number of outstanding territorial disputes with China, was upgrading its defenses on its islands in the East China Sea. These islands are undisputed Japanese territory and lie several hundred miles south of Japan's far larger and more populous "home" islands.

On November 27th, six Chinese bombers flew within Japan's exclusive economic zone and air defense identification zone near Miyakojima Island, on Japan's southern periphery. Although China did not violate Japanese airspace or sovereignty, the overflights were still a reminder of Beijing's operational capabilities in the region, and willingness to showcase its military assets even in a geopolitically sensitive context.

The US has made it clear that it wants the status quo to hold in the East and South China Seas.

One of the reasons for hte US's "pivot to Asia," the Obama administration's reorientation of military and diplomatic attention and assets to East Asia, was to check any potential Chinese expansionism in the region.

Increased US military assistance for countries like Vietnam and the Philippines, and the holding of high-profile military exercises with regional allies in Thailand andHawaii are all meant to indicate that the US intends to back countries that fear any future Chinese territorial encroachment.

But the diplomatic row over the B-52 overflights shows that this policy might carry some potential risks - and that there are points of possibly volatile opposition regardless of the countries' deep economic and diplomatic ties.