China’s territorial claims in the South China Sea, in defiance of a 2016 international arbitration ruling, is the “gravest external threat since World War II” to the Philippines, the acting head of the nation’s Supreme Court has said.

At a forum in Manila on Saturday, Senior Associate Justice Antonio Carpio encouraged Filipinos to ask the entire world to help convince the Chinese to abandon the belief China has a historic claim to almost the entire South China Sea.

“In China today, all the generals, admirals, professors, bureaucrats, diplomats, businessmen, they all grew up being taught from Grade One to college that they own the South China Sea since 2,000 years ago. It is in their DNA. They really believe it, honestly, sincerely. But it’s totally false,” Carpio said in a lecture entitled “Defending Philippine Sovereign Rights in the West Philippine Sea.”

“That’s why today, the Chinese government will not comply with the ruling of the tribunal because, if it does, then that delegitimizes them in the eyes of the Chinese people,” he added.

Citing results of extensive research on the issue, including material submitted to the Permanent Court of Arbitration in the Hague, Carpio called the Chinese government’s narrative about its historic claims in the South China Sea the “false history,” “fake news” and “disinformation” of the century.

According to Carpio, historical maps and documents from China showed it only started to expand its territorial claim beyond Hainan in 1932, when it protested French occupation of the Paracels.

And it was only in 1947 that China started to claim the Spratlys. A year earlier China occupied Itu Aba, the largest island in the Spratly archipelago.

The Philippines, on the other hand, included Scarborough Shoal and the Spratlys in its territory, based on a 1734 map, Carpio said.

But he noted “people in the West (have) started to believe” Beijing’s claims “because China is an old civilization.”

“I call this the gravest external threat to the Philippines since World War II because we will lose an area larger than the combined, total land area of the Philippines. … We are going to lose a huge maritime space. We lose all the fish, oil, gas and mineral resources here.”

Carpio said the Philippines should welcome the exercise by other nations’ militaries of freedom of navigation and overflight in the South China Sea.

Such activity by the United States, Australia, France, Britain, Japan, India and Canada actually enforces the Philippines’ victory at the Hague, and will prevent the South China Sea from becoming a Chinese lake, he said.

In an interview afterward, Carpio was asked about Philippine President Rodrigo Duterte’s policy toward Beijing, which is to set aside the arbitration award in favor of economic aid and investment from China.

He cautioned the government against conducting “joint exploration, development and exploitation” with China in the South China Sea.

“The constitution says the state shall have full control and supervision in the exploration and development of our natural resources. If it’s joint, then we are no longer in full control. … So we should avoid joint exploration and development,” he said.

Carpio said he was publicly issuing the warning because “once we cede our sovereign rights in a document, we cede it forever.”

“Even if the Supreme Court will say that the Philippines has no authority to do that, therefore it’s void, it will not bind China because China is not under our jurisdiction.”

But as China has already taken control over several features in the South China Sea and established air and naval bases on some of them, Carpio urged the Philippines “to prepare for the day that the Politburo of China will instruct” its “powerful navy” to “enforce the ‘nine-dash line’ as a national boundary of China.”