This fall, expect to hear a lot on the campaign trail about Iraq. Was it a mistake? Can we win? Is it worth it? Even some conservatives seem to wonder. But even after 18 months of negative media coverage, the bottom line is that the war in Iraq was worthwhile. Even critical.

Here's why: The United States faces several long-term threats, but the biggest by far is that posed by terrorists. According to Norman Podhoretz, editor at large of the highly influential Commentary magazine, the United States is engaged today in a fourth world war. The Cold War, he writes, was actually World War III. During the Cold War, we knew who the enemy was, and where the enemy was. We could even, to an extent, negotiate with the old Soviet Union. We could trust as long as we could verify.

Today's enemy is different. Al-Qaida's terrorists are slippery. It's difficult to determine where they are, so it's difficult to contain them. And there's no hope for negotiations. Osama bin Laden wants to build a new fascist regime. To succeed, he must first destroy the United States, so talking with us would be out of the question.

In addition, the Cold War ended when our enemy eventually gave up and went away. In this war, the enemy won't quit. We're going to have to destroy the enemy before it can destroy us.

That brings us back to the war in Iraq, which isn't a stand-alone war such as the first Persian Gulf war or the Spanish-American War. The war in Iraq is actually one theater of the greater war against Islamic terrorism, just as Europe in 1944 was simply a theater of World War II.

We needed to attack Iraq because, while many today deny it, Iraq was a direct threat to Americans. Our pilots were flying daily patrols in the U.N. no-fly zones over northern and southern Iraq and were frequently fired on by Saddam Hussein's military. These missions may have helped confine Mr. Hussein, but they were never going to topple him. Only direct military action could do that.

Also, whether or not he was formally allied with al-Qaida, there can be no doubt that Mr. Hussein was a staunch terrorist supporter. For example, he paid blood money to the families of Palestinian terrorists who had attacked Israeli targets. In this new world war, we can't afford to make distinctions between terrorist acts aimed at the United States and terrorist acts aimed at other democracies. As President Bush declared Sept. 20, 2001, "Either you are with us, or you are with the terrorists." That's the only way to fight this new war.

We've also heard a lot about the failure to find weapons of mass destruction. However, let's remember that we know Mr. Hussein had them at one time, and we know that he used them. He also cheated on inspections, leaving many weapons unaccounted for. Plus, he had the scientists, the technology and the money to quickly rebuild his WMD programs. Even the United Nations believed he had WMD. That's why the Security Council passed 17 separate resolutions insisting that Mr. Hussein disarm.

During the Iran-Iraq war, Mr. Hussein deployed chemical weapons several times. And our State Department lists 10 incidents of Iraqi chemical attacks between August 1983 and March 1988. All were launched against Iranian and Kurdish populations, resulting in casualty tolls in the tens of thousands. Mr. Hussein would have used these weapons against Americans, too, if he'd been given the chance. That's why our troops had to go in wearing protective clothing.

Our intelligence-gathering can and must be improved. But we also must face the fact that in this war, our intelligence will never be perfect, yet we must still be prepared to act. We can't wait until there's another 9/11 before we take action. Terrorist-supporting nations - as Iraq was, and as Iran and North Korea still are - must know we are serious about defending ourselves.

And that's another positive outcome of the war in Iraq, and our earlier war in Afghanistan. Soon, American troops will pull out of both places, leaving freedom and democracy where before there was only tyranny. The spread of freedom sends a powerful message to our friends and our enemies: We're not going away. Our ideas are sweeping the planet, while yours are being swept away.

As long as we're on the offensive, it'll be more difficult for al-Qaida to recruit, train or carry out missions against the United States. That's going to result in some direct confrontations with our enemies, as in Iraq, and it's going to result in some indirect confrontations, such as when we help nations such as Spain or Turkey track down terrorist killers.

But one thing is certain: We will win, in Iraq and in the broader war. The fate of Western civilization depends on it.

Ed Feulner is president of the Heritage Foundation in Washington.