Beijing is caught in a diplomatic bear trap of its own making. After trying to bully the Association of Southeast Asian Nations (Asean) into not discussing disputes over the South China Sea at a summit this weekend in Bali, the territorial dispute is becoming the meeting's focus.

The trouble proceeds from China's opening position: Its claim to "indisputable" sovereignty over 90% of the South China Sea. In reality, Beijing wants to gain maximum access to fish stocks and hydrocarbons...