The United States was accused of “coercive action that seeks to militarize the South China Sea region” by China’s Defense Ministry on October 27. The statement came after the guided-missile destroyer USS Lassen sailed within 12 nautical miles of Subi Reef—one of the artificial islands China has built in the South China Sea.

The Chinese Navy sent a guided-missile destroyer and a patrol ship to trail behind the uss Lassen as it passed the artificial island.

Unlike the name may suggest, the South China Sea belongs no more to the Chinese than the Gulf of Mexico belongs to the Mexicans. Disputes have occurred over the Paracel and Spratly Islands for decades, but they have become heated in the past few years as China has built artificial islands and tried to restrict fishing by the surrounding nations. The Philippines, Vietnam, Malaysia and Brunei all claim parts of the South China Sea region.

Foreign ministry spokesman Lu Kang said that if the United States continued to “create tension in the region,” China could conclude that it may have to “increase and strengthen the building up of [its] relevant abilities.”

According to the United Nations Convention on the Law of the Sea, the uss Lassen did not break any laws or “seek to militarize the South China Sea.” The convention states that 12-nautical-mile limits cannot be set around man-made islands built on previously submerged reefs.

Reported spotting of mobile artillery vehicles in the region and runways on the islands, which can accommodate fighter jets and large transport aircraft, indicate that the Chinese could use the islands militarily if needed. Washington is worried about this development, but according to Stratfor, “China is well aware of U.S. reluctance to escalate the conflict and takes advantage of it to keep expanding its presence.”

In regards to further patrols in the South China Sea, a U.S. Defense official said, “I would expect that this becomes a regular operation.” China is yet to show any signs of slowing activity in the South China Sea, even with the challenges from other nations in the area.

The South China Sea is just one arm of the expanding Chinese superpower, which reaches across world economics and politics. To find out more about that expansion, and the nations it is destined to unite read “The Rise of Asia.”