ON SEPTEMBER 11, THE United States will observe the fourth anniversary of its entry into the war on terrorism. The war has already exceeded by a few months our entire time of involvement in World War II. It's hardly too early to take stock of what we've learned about the nature of the war and the stakes involved in its outcome.

First, this is a world war. From North America to Indonesia, with many points of impact in between, the war has drawn in dozens of nations and billions of people.

Second, the war has taken the form of a civil war in increasing numbers of countries. From the beginning its hallmark was a convulsive upheaval within the Islamic religion. In its first wave, the clash within Islam led to discord among different kinds of Muslims in such countries as Pakistan and Turkey. Recent events in the Netherlands and Britain have underlined its potential for civil violence within every non-Muslim democratic country with a sizable minority of Muslims.

Third, to a surprising degree, the war has remained fundamentally bipolar. Its two poles are the United States and the violent wing of Sunni Islam symbolized and led by Osama bin Laden and his terror vehicle, al Qaeda. At first glance this attribute may seem to contradict elements of the first two, which are about the war's global reach and multiplicity of players. But it does not.

A good analogy is to the Cold War, which from 1945 to 1991 drew in billions of people and dozens of governments, but at root was always a bipolar conflict between the United States and Soviet-style communism based in Moscow. The bipolarity of the Cold War is underlined by the fact that survival of the main Asian Communist regimes after the 1991 dissolution of the Soviet state led no one to say the Cold War was continuing.

Nonetheless, during the course of the Cold War there was no shortage of elite analysts willing to argue the reverse, or at least that world politics was getting less and less bipolar. The implication, almost always, was that hawkish leaders like Ronald Reagan were "simplistic" in their belief that undoing or neutralizing Soviet power was the key to ending the Cold War.

Similarly, from the beginning of the war on terrorism, many if not most analysts, particularly the huge portion hostile to George W. Bush and dovish on the war, have posited a multiheaded enemy that will suffer a setback on one front only to pop up on another. The implication is that our most unarguable victories (such as overthrowing the Saddam Hussein tyranny in Iraq) are exercises in futility or (worse) counterproductive provocations that enhance recruitment of anti-American terrorists all over the world. If this is true, if the enemy is so ubiquitous and diffuse, why even try for a victory?

Yet the movements and statements of our most indisputable enemies have increasingly pointed in the other direction, toward bipolarity. Organizations claiming to be branches of al Qaeda are currently fighting the United States in Iraq and our key ally, Britain, in London. Like the Madrid bombings of March 11, 2004, which ejected Spain from Iraq, the London terror bombs aim to get Britain out of Iraq and out of its strategic alliance with the United States. Thus the two chief protagonists in the war, the United States and al Qaeda, are in complete agreement that Iraq is the central front of the global war, and that getting the United States' chief ally out of Iraq would thus be an enormous coup for our enemies.