Japan incorporated the Senkaku Islands in 1895, declaring the uninhabited islets in the East China Sea to be "terra nullius," or land belonging to no one, by international law and with no traces of Chinese control found.

But if the islands are actually owned by China, as Beijing has repeatedly claimed, Japan's claim could be seriously undermined. So what do historians think about the issue?

Chinese scholars have argued that China recognized the islands as the Diaoyu and used them as part of their "sea defense areas" near Fujian Province as early as the 16th century. A map in a book compiled by Gen. Hu Zongxian in 1561 seems to corroborate this claim.