By Rodger Baker Vice President of East Asia Analysis Sept. 29 will mark 40 years of normalized diplomatic relations between China and Japan, two countries that spent much of the 20th century in mutual enmity if not at outright war. The anniversary comes at a low point in Sino-Japanese relations amid a dispute over an island chain in the East China Sea known as the Senkaku Islands in Japan and Diaoyu Islands in China. These islands, which are little more than uninhabited rocks, are not particularly valuable on their own. However, nationalist factions in both countries have used them to enflame old animosities; in China, the government has even helped organize the protests over Japan's plan to purchase and nationalize the islands from their private owner. But China's increased assertiveness is not limited only to this issue.