This year marks the 40th anniversary of the normalization of China-Japan diplomatic ties. Common sense would suggest Japan should join China's efforts to nourish the tree of friendship and make it grow even healthier.

Instead, Japan has chosen to ratchet up the dispute with China over the Diaoyu Islands.

Moreover, Japan's Kyodo News Agency reported that an official from the State Department of the United States said the Diaoyu Islands fall within the scope of Article 5 of the US-Japan Treaty of Mutual Cooperation and Security, as the island group has been under the administrative control of Japan since they were included as part of the reversion of Okinawa in 1972.

The absurdity of these remarks is obvious.

Japan is trying to use a bilateral deal with the US after World War II to form the legal basis for its self-proclaimed sovereignty over the Diaoyu Islands. But a private deal between Japan and the US has no bearing on China's sovereignty over the islands.

The historical evidence, including World War II documents, prove that China's claim is irrefutable.

China was the first to discover and explore the Diaoyu Islands and obtain sovereignty by occupation. No later than the Ming Dynasty (1368-1644), the islands had been discovered, explored and named by the Chinese. All these are well documented in black and white.

Japan arrogated the islands along with Taiwan and its other surrounding islands and incorporated them into Okinawa prefecture as Japanese territory after its victory over the Qing Dynasty (1644-1911) in the 1894-95 war between the two countries.

But the islands automatically reverted to China from the time Japan unconditionally surrendered and accepted the Potsdam Proclamation at the end of World War II.

The Potsdam Proclamation, issued in 1945 by the allies, stipulated that Japan must carry out the clauses of the Cairo Declaration of 1943. This stipulated that Japan should return to China all the territory it had seized from it during and after the 1894-95 war.

The Potsdam Proclamation and the Cairo Declaration are international treaties. No one, except some in Japan and the US with their own agenda, would argue that a security pact between Japan and the US takes precedence over these two international treaties.

Any private deals made between the US and Japan concerning the Diaoyu Islands are illegal and invalid.

Instead of making provocative moves to assert control over territory that belongs to another country, Japanese politicians should follow the example of those who have helped nourish the tree of Sino-Japanese friendship over the last 40 years.