Obama went to Tokyo to reassure Japan that, should China attempt to seize its Senkaku Islands, America will fight at her side.

He reassured Seoul of our commitment to defend South Korea.

He went to Manila to reassure the Filipinos, who threw our Navy out of Subic Bay at the end of the Cold War, that America will be there in any clash with Beijing in the South China Sea.

Yet, as Clyde Prestowitz writes in the Financial Times, while we are committed to go to war to defend all three countries if attacked, none of them is obligated to go to war if we are attacked.