A North Korea equipped with nuclear ICBMs might change the equation: Could the Americans still be counted on to fight for Japan if doing so carried the risk of losing Los Angeles or New York?“When North Korea has been armed with nuclear weapons, the security regime under the current Japan-U.S. alliance, however strong, may be unable to fully protect Japan’s safety,” said a security-related Japanese government official.

Source: Will North Korea set off a new arms buildup in Asia?