TO CHINA, Japan's move to "nationalise" the uninhabited Diaoyu/Senkaku islands at the centre of an increasingly heated tussle between them is akin to someone seizing possession of something whose legal ownership is still being disputed.
One party's action is sure to trigger a reaction from the other. It did.
Now, for the first time, China is challenging Japan's sovereignty over a group of islands which used to be called Ryukyu islands and which now make up Okinawa prefecture.
Like the Diaoyu islands, the Ryukyus also lie in the East China Sea, between Japan's Kyushu island and Taiwan.
On Sept 14, a commentary in the People's Liberation Army (PLA) Daily asserted that "even the Ryukyu islands do not belong to Japan, under international laws governing the post-World War II order".
The Ryukyu islands came under the United States' civil administration from 1945 until 1972, when the Americans handed over control to the Japanese.
The PLA Daily's commentary stopped short of saying that the Ryukyus belong to China. But Chinese historical records would appear to support such a claim.
The earliest records of the Ryukyu islands can be found in the Book of Sui, written in AD621 to record the history of the Sui Dynasty (AD581-617). The Ryukyus used to be a tributary state of China. The name Ryukyu, in fact, originates from Liuqiu, also spelt Liuchiu and Lewchew, a name the Chinese gave to the islands.
Ryukyu historical records showed that from 1383 onwards, its kings derived their mandate to rule the islands from the Chinese emperor. This continued for nearly five centuries until 1879, when Japan annexed the islands and called them Okinawa prefecture.
This is well documented in historical records, which is why when the US-led Allied powers held discussions on "restoring territories", referring to Chinese territories that Japan had taken by force, both the Ryukyus and Taiwan were included.
According to American official records (Roosevelt-Chiang Dinner Meeting, Foreign Relations of the United States, 1943), then US President Franklin D. Roosevelt asked about China's intentions regarding the Ryukyus at a private dinner meeting with Chinese Generalissimo Chiang Kai-shek on the sidelines of the 1943 Cairo Conference.
"The President then referred to the question of the Ryukyu islands and enquired more than once whether China would want the Ryukyus.
"The Generalissimo replied that China would be agreeable to joint occupation of the Ryukyus by China and the United States and, eventually, joint administration by the two countries under the trusteeship of an international organisation."
The Soviet Union's leader Josef Stalin shared the same view about restoring territories to their rightful owner, China.
A paragraph in a Memorandum of the White House Conference in January 1944 read: "President Roosevelt also recalled that Stalin is familiar with the history of the Liuchiu islands and that he is in complete agreement that they belong to China and should be returned to her, and further that the civil administration of all islands now controlled by Japan should be taken over by the United Nations."
These two records amply show that the common international understanding at the time was that the Ryukyus belonged to China.
In the Cairo Declaration announced by the Allied powers on Dec 1, 1943, one section stated that "Japan shall be stripped of all the islands in the Pacific which she has seized or occupied since the beginning of the first World War in 1914, and that all the territories Japan has stolen from the Chinese, such as Manchuria, Formosa and the Pescadores, shall be restored to the Republic of China. Japan will also be expelled from all other territories which she has taken by violence and greed."
Most World War II historians agreed that the "territories" in the last sentence referred to the Ryukyus. It was not specified because the Sino-US joint trusteeship had not been ironed out yet.
On July 26, 1945, came the Potsdam Declaration setting out the terms of the Japanese surrender. Paragraph 8 stated: "The terms of the Cairo Declaration shall be carried out and Japanese sovereignty shall be limited to the islands of Honshu, Hokkaido, Kyushu, Shikoku and such minor islands as we determine."
Then on Feb 2, 1946, US General Douglas MacArthur, Supreme Commander for the Allied Powers, issued a statement limiting Japanese territories to the four major islands and about 1,000 small islands situated north of 30 deg latitude. Since the Ryukyus, and also Diaoyu islands, lie south of 30 deg latitude, they are, legally speaking, no longer Japanese territory.
But the defeat of Generalissimo Chiang's Kuomintang by the Chinese Communist Party (CCP) in 1949 after a civil war prompted the US to change its mind.
In a bid to contain communism, the US set up an island chain of defence from the Aleutian islands in the northern Pacific to Java in the south. The Ryukyus became a pivotal link centrally located in this arc-shaped defence perimeter against communism.
However, the US has never challenged China's sovereignty over the Ryukyus and Diaoyu islands.
When Washington handed the islands to Tokyo in 1972, it had stressed that it was handing over only the administrative power to Japan, and that it held no position regarding their sovereignty.
It also maintained that the sovereignty issue was to be settled between Beijing and Tokyo.
The PLA Daily's commentary was a reminder to Japan that should China find itself forced into a corner, it may have no choice but to challenge Japanese sovereignty over not only Diaoyu islands but also the Ryukyus.
China has a strong legal basis. Article 3 of the Sept 29, 1972 Sino-Japanese Joint Statement, which paved the way for the two countries to establish diplomatic ties, stated that Japan "shall firmly abide by the principles under Article 8 in the Potsdam Proclamation".
In other words, Tokyo is obliged to respect the 1943 Cairo Declaration, the 1945 Potsdam Declaration and the so-called MacArthur Line defining the extent of Japanese sovereignty.
Japan had better not cross the line.