China’s claim to islands in the East China Sea known as Diaoyu (‘fishing’) dates back to antiquity, according foreign ministry spokesman Geng Shuang. "No matter what anyone says or does, it cannot change the fact that the Diaoyu Islands belong to China, and cannot shake China's resolve and determination to protect national sovereignty and territory," Geng stated in Beijing.
Diaoyu/Senkaku have been uninhabited since 1940, when Japanese entrepreneur Koga Tatsushiro closed down a fish processing plant that employed 200 people. Since the US Senate ratified the Okinawa Reversion Treaty in 1972, administration of the islands was transferred out of the hands of the US government to Ishigaki, a Japanese city, in Okinawa Prefecture. The US has recognized Japan’s stake since this transfer. Taiwan considers the cluster of islands as part of Yilan County while China also classifies the islands as part of Yilan County, but it also considers Taiwan a Chinese province.
Trump’s affirmation of allegiance with Japan regarding the disputed islands continues President Barack Obama’s diplomatic legacy in the region. In 2014, Obama pledged to send armed forces to Japan’s aid if Chinese forces were to occupy Senkaku. Washington rejects any "unilateral attempts to undermine Japan’s administration of the islands," Obama told local Japanese media in 2014, and at least on this particular issue the Obama and Trump administrations are in harmony.
"I just want everybody to understand and fully know that the United States of America stands behind Japan, its great ally, 100 percent," Trump said in a joint statement.