The United States cannot stop nuclear proliferation, even though Japan and others will expect it to keep trying. The Nuclear Nonproliferation Treaty (NPT) has allowed North Korea and Iran to develop nuclear weapons on the sly. What will Japan conclude from this?
Japan, in order to balance the rapidly growing power of a nuclear-armed China, will have to acquire offensive capabilities. That may include nuclear weapons, although that is not yet inevitable.
The so-called breakthrough in the six party talks on North Korea did not last even 24 hours. Last week, the board of the International Atomic Energy Agency passed a resolution saying Iran had violated the NPT by secretly developing nuclear weapons. But lacking consensus on the board, the IAEA could not report Iran to the United Nations Security Council, where sanctions might be imposed.