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"The Americans are serious," the head of the Russian delegation told the North Koreans in a meeting in Beijing in September 2005. "You see this? This is called a negative security assurance. We tried to get this from them throughout the Cold War and were unsuccessful."

We'd been negotiating since 2004 -- the famous "six-party" talks featuring the United States, China, Japan, Russia, South Korea and, of course, the North -- trying to hammer out an agreement that would end Pyongyang's nuclear program. The issue of the moment was a clause that had just been approved in Washington, stating that the United States "would not attack North Korea with nuclear or conventional weapons."

It was a big step for the Americans, and the Russians, at least, recognized that. It meant that...