Sandwiched between regional rivals like South Korea and Japan and facing military encirclement by the United States, North Korea is the only country that challenges the US global agenda. But Pyongyang’s brazen military muscle flexing is disturbing the diplomatic calculations of Asia on an unprecedented scale. Its recent long-range missile tests (one was an embarrassing failure) and threats to reduce South Korea’s capital Seoul to ashes in a storm of steel and fire in case of a US attac