A large American fleet shows up in the eastern isles of the Philippines in order to enforce its claim of the Philippines. It is not aggressive with Japanese vessels and does not land any marines.
America says one word a phrase: the people's will.
Phillipinnes can choose its fate: under the protection of America with almost nearly direct sovereignty, under the protection of Japan (and probably assimilation into the Japanese realm), or as an independent state.
Two of those options America will support, but the third is a shrug "ok".
see: bigger than japan's fleet