China and the Philippines are at loggerheads over which owns a variety of mostly unoccupied islands, reefs, and shoals in the South China Sea. It is the sort of place where a war could break out between China and the Philippines, a former colony and more-or-less client of the U.S. See a Reuters article on the Yahoo News site for more.
China takes the attitude that, because they are the only large, seriously militarized nation bordering the region, any small islands, etc., belong to them. This "I'm the bully in the neighborhood" posture has put China at odds not only with the Philippines, but also with Vietnam, Japan, Taiwan, Brunei, India and Malaysia.
Several of these less militarized nations are U.S. "friends" or allies. If they get knocked about by China and ask for help, we either help them and maybe get drawn into a war with China or don't help them and look weak.
Both are bad options.
