Why has Russia teamed up with China in the South China Sea?

China will hold joint military exercises in the South China Sea with another eastern power and US rival, as the United States continues to insist China comply with an international ruling that denies its territorial claims in the region.  

Russia and China will hold the joint exercises in September, Yang Yujun, a spokesman for the China Defense Ministry, said in a news conference Thursday. The land and sea exercises will be “routine,” and will not “target any third party,” he said.

The drill will further forge the “comprehensive strategic partnership of coordination, deepen pragmatic and friendly cooperation between the two militaries,” said Mr. Yang, “and enhance the capabilities of the two navies to jointly deal with maritime security threats."

Though Yang implied the exercises will not be directed at the US, the two countries have gone tit for tat in displays of force there. The exercise, then, personifies further Russian involvement in the dispute, supporting China’s position, and contesting what it sees as US interference in yet another part of the world.   

Yang didn't disclose where the exercises will occur in the South China Sea, and some parts of the sea are not disputed. Much of it is, however.

China lays historical claim to the “nine-dash line,” which appears on official Chinese maps, and spans about 80 percent of the sea. Brunei, Malaysia, the Philippines, Taiwan, and Vietnam all have conflicting claims in the South China Sea, which sees $5 trillion in trade pass through it each year.  

Russia has a history of supporting Chinese territorial claims in the South China Sea, while criticizing outside involvement there, a reference to Chinese allegations the US is “meddling” there, as Russia Today wrote. Russia has also supported China’s response to the ruling by the Permanent Court of Arbitration in the Hague, Netherlands. The court found China had no basis for its expansive claims to territorial waters around the Philippines. Many of China's claims are the result of building it has done on top of reefs and rocky outcroppings to give it international rights to develop the waters surrounding these "islands." The court denied these claims, along with many of China’s historic claims in the nine-dash line.

Following the ruling in The Hague on July 12, Russian Prime Minister Dmitry Medvedev backed China’s demand for bilateral talks to solve the dispute, as opposed to adherence to the court ruling that denied China’s claims there. According to the state-sponsored Xinhua News Agency, Mr. Medvedev also criticized any “interference from forces outside the region,” a likely reference to the US.

China has frequently blamed the US for inciting tension in the region through military patrols, alleging the US has taken sides in the dispute against it.

The US has said it its patrols are an assertion of the right to freedom of navigation in the South China Sea, and denies taking sides in the territorial disputes.

This isn’t the first time China and Russia have held joint military exercises together. With Yang referring to it as an annual tradition, the two countries held exercises in the Mediterranean and Sea of Japan. Russia even agreed to participate in a 10-country military parade through Beijing in September to commemorate the 60th anniversary of China's victory over Japan in World War II, the Associated Press reported in August. The Sea of Japan is also the site of islands Russia and Japan contest. Russia controls the islands off Hokkaido, but Japan lays claims to them.

Russia and China have also allied in their positions on the crisis in Syria, supporting President Bashar al-Assad’s claims there, rather than supporting the rebel-backed forces fighting against him.

The two countries have also been outspoken against US deployment of an anti-missile system, the Terminal High Altitude Area Defense (THAAD), in South Korea. The US has said the missile system is meant to act as a shield against any North Korean attack. But China, in particular, has worried that the system’s radar would be able to track its military capabilities.    

This report contains material from the Associated Press and Reuters.