They've actually had some successes. UN and it's associated agencies can be a mixed bag. UNESCO = useless, WHO = pretty good.
You don't really hear much about the successful border dispute resolution because they don't result in wars.
South China Sea is so small the officially allowed offshore claims overlap. You need some sort of non-state party to resolve the dispute.
Former President William Jefferson Clinton told the United Nations he wanted to put the United States into a "web" of treaties to set the ground rules for "the emerging international system."