In the 2003 Academy Award-winning documentary “The Fog of War,” former Defense Secretary Robert McNamara imparts lessons he learned from overseeing the Vietnam War. One key lesson, Mr. McNamara says in the film, is that it is imperative to understand why the enemy fights. That lesson should be applied to U.S. dealings with the seemingly unpredictable nation of Iran. Iran’s recent missile tests are the latest evidence that a more sophisticated posture than that maintained by President Bush is needed in parrying such threatening gestures.

In the documentary, Mr. McNamara recounts meeting with a former North Vietnamese military leader many years after the Vietnam War ended. The man insisted, Mr. McNamara said, that the U.S. wanted to turn his country into a colony. As absurd as that view was, it explains the motivation of the North Vietnamese and Viet Cong, Mr. McNamara suggests. That fear was not absurd given that Vietnam had been colonized and subjugated by China, Japan and France.

Iranian President Mahmoud Ahmadinejad may be caricatured as a madman by the Bush administration, but it is more likely the Iranian leader is playing chess with the U.S. The missile tests, intelligence officials say, do not portend a threat to the U.S., nor do they suggest Iran is any closer to developing a nuclear arsenal. But the consequences are potentially dire if the wrong counter gambit is used.

Three factors open windows through which Iran’s behavior can be understood: Israel, Iraq and the Iranian people.

Israel is the hub around which the Middle East’s political turmoil swirls. Mr. Ahmadinejad has played the anti-Israel card by denying the Holocaust and refusing to acknowledge Israel’s right to exist. But much of this blustering likely comes from Iran’s fears of Israel launching an attack on it. A step toward calming Iran would be to assure it that the U.S. will restrain Israel from pre-emptive strikes.

And speaking of preemptive strikes: the U.S. invasion and occupation of Iraq has recast Middle East political dynamics; it’s what the Bush administration intended, but the picture is not what it anticipated. With Iraq’s stability in question, Iran has cause to worry about its former enemy and neighbor. In his 2002 State of the Union speech, Mr. Bush named Iraq, Iran and North Korea the “Axis of Evil,” and said they were worthy of U.S. enmity. Fifteen months later, the U.S. invaded the first nation on that list; Mr. Ahmadinejad could reasonably wonder if his nation was next, prompting him to arm.

Lastly, Iran’s military muscle flexing may have as much to do with internal politics as with intimidating the U.S. and Israel. Mr. Ahmadinejad is a hard-liner in a country with a burgeoning moderate populace; an entire generation has come of age since the Iranian revolution of 1979, and it is more open to normalized relations with the West. Mr. Ahmadinejad may be using missiles to stir patriotism and solidify power.

Just as North Korea’s missile tests led to heightened diplomatic overtures from the U.S. and its allies, Iran should be the focus of U.S. negotiations which consider that country’s place in the fragile Middle East web. It should not have taken missile tests to urge such attention.