Japan seeks closer military cooperation with U.S. Japanese Defense Minister Satoshi Morimoto has called for closer military cooperation given Chinaâ€™s naval expansion in the East and South China Sea as well as terrorism and cybercrime emanating from China. Japan hopes to reinforce the existing Treaty of Mutual Cooperation and Security between the United States and Japan, which has been in effect since January 1960. Among other things, the U.S. is obligated to come to Japanâ€™s assistance in the event of an armed attack. Japan is the second largest economy in Asia and has Asiaâ€™s most efficient military in the region, even though it is smaller in size to that of China. Yet, Tokyo has its own issues with Beijing over ownership of the Diaoyu/Senkaku Islands.