Commentary: Is the US obligated to defend Japan’s Senkaku Islands against China? probably.
09/21/12: Julian Ku argues on Opinio Juris that the US may be obligated to protect the Senkaku Islands. As things continue to get ugly between China and Japan over the Senkaku/Diaoyu Islands, the U.S. has tried to stay out of the way. Still, although the U.S. has tried to stay neutral on the territorial dispute, it appears the U.S. is obligated by treaty to defend any incursion by China into the Senkaku/Diaoyu.