Why US meddles in Diaoyu Islands issue?

Recently, the U.S. Senate has appended to National Defense Authorization Act for Fiscal Year 2013 the additional clause which specifies that the Article V of Japan-US Security Treaty is applicable to the Diaoyu Islands issue. It is rare an additional clause on territorial disputes between other countries is attached to National Defense Authorization Act. If the Act finally passes in the U.S. House of Representatives, it means the United States will take intervention measures or even directly deploy armed forces once China and Japan clash over the Diaoyu Islands issue.

Japanese right-wing forces have cast shadows on the Diaoyu Islands issue. Why does the United States meddle in the issue at this moment?

Originally, the U.S. public attitude toward the Diaoyu Islands is not to take side on its sovereignty. However, the Japan-US Security Treaty can be applied to the whole region of the Diaoyu Islands since Japan exercises jurisdiction over them. Obviously, the new move of the U.S. Senate does not aim to strike up the same old tune.

First, it is the requirement of U.S. foreign policies. Facing the economic downturn and the complex international situation, the United States runs short of ways to deal with too many problems. Some allies begin to doubt U.S. responsibilities, obligations and abilities. Therefore, it is imperative for the United States to establish authority and trust among its allies.

Japan is U.S. largest ally in Asia Pacific. U.S. emphasis on its responsibility of protecting Japan does not only pacify Japan but also relieve other countries in Asia Pacific which intend to rely on the United States, which is conducive to its "rebalancing" strategy in Asia Pacific.

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