Rome -- Here the sun is shining, the quiet Tiber suggests lazily that it has seen everything there is to see in this world; the streets are thronged with tourists (including this columnist); the locals are amorous; and the food is delicious. Here, perhaps even more than in the United States, one could easily slip into the comfortable feeling that we are at peace. Explaining the Obama administration's departure from some Bush interrogation techniques, Director of National Intelligence Dennis Blair described reading about those methods "on a bright, sunny, safe day in ... 2009."

Well, it feels peaceful now. But to paraphrase the great Anonymous: The wise man learns from other people's mistakes. The sensible man doesn't make the same mistake twice. And the fool fails to learn from his own mistakes. History (and being in the Eternal City makes one more than usually conscious of the past) affords thousands of examples of the folly of falling into complacency when a threat seems to have temporarily abated. Troy arguably fell for this at the hands of the Greeks. Europe's democracies deluded themselves that Germany wanted peace as much as they did following the catastrophic First World War. Israel failed to keep its guard up after the 1967 war and was caught flat-footed (for a time) by the attack that came in 1973. Fill in your own favorite examples.

This week the Democratic People's Republic of Korea has exploded what looks to be a real nuclear weapon (the last explosion left some experts in doubt) and also launched a short-range missile as, what, an exclamation point perhaps? This destitute little redoubt of crazed Stalinism now has something of value to sell to the highest bidder. And while we're contemplating that grim picture, consider that there is a failure here.

We've heard incessantly since 2006 that George W. Bush's handling of the Iraq War represented the failure of armed force. And while it is certainly true that President Bush waited about two years too long to fix the problems in post-invasion Iraq, the much-overlooked reality is that developments in Iraq now seem to be on track for a happy ending. Even if you believe that the price was too high in blood and money for the results obtained, you cannot reasonably argue that the whole enterprise was a failure. In place of a genocidal aggressor in Iraq, we now have something that looks more democratic than any other Arab state.

The exclusively diplomatic approach, by contrast, has suffered a complete and total failure in the case of North Korea. This was not a failure simply of the Obama administration (U.S. Special Envoy Stephen Bosworth last week noted that the Obama administration is "relatively relaxed" and that "there is not a sense of crisis") but also of the Bush and Clinton years. All of these administrations followed essentially the same policy. Remember former President Jimmy Carter (Clinton's informal envoy) proudly boasting of the "Framework Agreement" they had achieved? The U.S. agreed to provide North Korea with fuel oil and two light-water nuclear reactors in exchange for the DPRK's promise to suspend its nuclear weapons program. When asked, a couple of years on, about North Korean violations, Secretary of State Warren Christopher was reassuring: "The Framework Accord between the United States and North Korea has proved to be quite durable through a rather long period of time as we have gone through the steps called for by the Accord. The United States has been furnishing oil and KEDO (Korean Energy Development Organization) has been moving forward in its processes. When I met with Foreign Minister Gong recently we agreed it was very important to preserve the Framework Accord because through it we have frozen the North Korean nuclear development ..."

Clinton's next secretary of state was no less solicitous of agreements. Madeleine Albright spent the last days of the Clinton presidency posing with Kim Jong-Il in Pyongyang.

The Bush administration, after some initial tough talk, caved to the State Department's diplomacy track. In its final months, the Bush administration removed North Korea from a list of terror-sponsoring states. No one has ridiculed this more pungently than former U.N. Envoy John Bolton:

"In the weeks before being delisted, North Korea expelled international inspectors, first from its Yongbyon plutonium-reprocessing facility and then from the entire complex. It moved to reactivate Yongbyon and to conduct a possible second nuclear-weapons test, and prepared for an extensive salvo of antiship and other missile capabilities. All of this the Bush administration dismissed as North Korea's typical negotiation style."

The fruits of this path of "diplomacy only" -- blindly pursued by three presidents -- are now clear. But those so eager to learn lessons from mistakes in Iraq will probably be deaf to this one.