Japan has put its foot down — at least in writing — over China's attempts to assert greater control of the South China Sea.

In an outline of a defense white paper due to be released at the end of July, Japan calls China's efforts to lay claim to the much-disputed Spratly Islands "high handed." The diplomatically sharp words come in the wake of China's reclamation efforts of the islands, which have included laying the foundations of a military base on Fiery Cross Reef at the western edge of a part of the South China Sea fittingly named Dangerous Ground.

Over the past year and a half, China has built up seven reefs in the region, adding 800 hectares — about three square miles — to islands and putting an airstrip and the beginnings of the base on Fiery Cross Reef. China has claimed that its structures in the South China Sea are for civilian purposes — or at most for a defensive military role — and would benefit other countries. But Japan's fight with China over the Senkaku Islands in the East China Sea has seemingly left them wary of Beijing's intentions.

Japan's decision to act on this wariness so stridently, however, is a recent phenomenon. Prime Minister Shinzo Abe has been pushing for legislation that would allow Japan to participate in collective self-defense for the first time since World War II.

"[This is] a shift that's been coming," Kelley Currie, a senior fellow with the Project 2049 Institute, told VICE News. "The language is definitely stronger, and the whole effort around reinterpretation to the self-defense constitution has been a response to the multi-year trend of the Chinese being more aggressive and pushing their military advantage in the region."

Japan isn't the only one pushing back against China's expansion in the region. The Philippines is taking China to court over territorial claims to the South China Sea, with top Filipino officials appearing at The Hague to argue their case before a United Nations arbitral tribunal. China has called it a "political provocation."

"The Chinese take kind of a Leninist approach to these things," Currie said. "They probe with the bayonet until they hit steel, and then they'll stop. When they start to see that people are serious about pushing back, then they will back off a bit."

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Other than the United States, Japan is the only nation that can truly challenge China in the region militarily.

"China is actually very worried about Japan and how far Japan might go," Michael Auslin, resident scholar and director of Japan Studies for the American Enterprise Institute, told VICE News.

While Japan has a strong army and navy, and can defend its own islands and interests, in a broader conflict like the one developing in the South China Sea, Japan is still relatively limited, Auslin says. And China's rivals in the region tend to look to the US to help maintain stability.

"The US plays a unique role, because it's not an Asian nation, as a relatively distant and disinterested outsider there," Auslin said. "The interest we have is not territorial, it's not to benefit ourselves in any way other than maintaining this open trade order that we benefit from economically, but not in any of the traditional ways that usually cause war."

China, however, doesn't see things in quite the same way. For years, the superpower has asked the US to mind its own business, viewing the dispute over the South China Sea as an Asian matter.

"We have security relationships with these countries, with Japan, with the Philippines, we have treaty alliances, and we'll continue to do these exercises in the South China Sea, and the Chinese will consider it extremely provocative," Currie said. "But we're just responding to things that they're doing that are extremely provocative with [relatively] small things."

The US likely further "provoked" China after the US commander of the Pacific Fleet, Admiral Scott Swift, took a seven-hour surveillance flight from the Philippines over the South China Sea this past weekend. Swift said that the Pacific Fleet is "ready and prepared to respond to any contingency the president may suggest would be necessary" in the region. The Chinese embassy in Manila offered no immediate response.