'The United States is closely monitoring the political and diplomatic struggle over the Pinnacle Islands. Historically, US involvement in the area is extensive. The islands were occupied by the United States from the end of World War II until 1972, when they were "returned" to Japanese control. Both China and Taiwan dismissed this transfer of authority as a violation of Chinese sovereignty.
Secretary of State Hillary Clinton stopped in Japan on her way to the recent ASEAN meeting in Cambodia. She inquired about Japanese plans to "nationalize" the islands, with apparent concern for Sino-Japanese relations. She then met with the Chinese foreign minister at the sidelines of the ASEAN summit, with Clinton stressing that the US won't "take sides in disputes about territorial or maritime boundaries". 
This is a pointed change in tone from earlier that week, when a State Department official said that the US would be required to come to Japan's aid in case of attack by a third party on the disputed Islands: "The Senkakus would fall within the scope of Article 5 of the 1960 US-Japan Treaty of Mutual Cooperation and Security because the Senkaku Islands have been under the administrative control of the government of Japan since they were returned as part of the reversion of Okinawa in 1972," said the unnamed official. 
Article Five of the 1960 US-Japan Treaty is essentially a mutual-defense clause. It is a cornerstone of US Asia policy, cementing the alliance between the US and Japan. However, its application in case of skirmishes over the Pinnacle Islands could lead to disastrous consequences.
The US neither wants to appear as an ineffective ally, nor to risk World War III over a small maritime clash. Clinton's efforts to reach out to the Japanese and Chinese governments, as well as her claims that the US does not favor one territorial claimant over another, are part of a concerted effort to disuse a potential powder keg.'