The last U.S. combat forces exit Iraq this week. The argument over Iraq is still nowhere near finished.

The costs of the Iraq war are evident to all. Now consider an alternative universe, with different choices — and weigh those costs.

As president George Bush assessed his options in 2002, oil prices averaged less than US$23 a barrel. These low prices had squeezed Iraq’s income and therefore Saddam Hussein’s power.

But war or no war, the price of oil would zoom upward in the 2000s. China had more than 90 times as many cars on the road in 2010 as in 1990. Chinese oil imports grew 7.5% a year, Indian oil imports only slightly less fast. Soaring oil demand from China and India pushed prices higher and higher: averaging US$28 a barrel in 2003, $38 in 2004, $50 in 2005, $64 in 2007 and $91 in 2008. A surviving Saddam would have been a wealthy Saddam.

Not only wealthy, but empowered. The international sanctions regime had collapsed in the late 1990s, freeing Saddam to import more or less what he wished, potentially including the instrumentalities of war.

As we now know, Saddam Hussein had not in fact succeeded in reconstituting his nuclear program as of 2003. But Saddam did try twice before to gain a nuclear weapon: He had a program in the 1970s that was wrecked by Israeli airstrike in 1981, and then a second program in the 1980s that was discovered by UN arms inspectors after the First Gulf War.

It seems incredible that a Saddam still in power in the 2000s, unconstrained by sanctions and enriched by Chinese and Indian oil money, would not have tried a third time. Even if Saddam had not sought to build a nuclear bomb, an additional $100 billion or so in annual oil revenues would still have paid for a lot of mischief in the Middle East.

Would Saddam have competed with Iran to fund Hamas? Would he have made common cause with Venezuela’s Hugo Chavez to support anti-government insurgents in Colombia? Would Iraq have offered haven to al-Qaeda terrorists escaping Afghanistan?

A Saddam-ruled Iraq would not have been a quiet or comfortable place. And when the regime finally did end, it would have ended violently. When the U.S.-led coalition overthrew Saddam, violence erupted between Sunni and Shiite Iraqis, leading to an estimated 100,000 civilian deaths. Does anybody imagine that things would have gone better if the regime had ended instead with a Saddam assassination or heart attack?

Blame the Americans, if you like, for not having a better plan ready to contain the violence. But it was not the United States that caused the violence, much less the United States that committed the violence.

Now Iraq is finding its way to stability. For all the country’s many problems, it has an elected government and an effective post-Saddam security force. Would this have happened in the absence of international forces? Or would Iraq have looked like Lebanon between 1975 and 1991, a cauldron of sectarian violence for a generation, with casualties of many multiples of 100,000? Again: We cannot know, but the ugly scenarios are the most plausible.

With foresight, everybody would fight the Iraq war differently. That is always true for any war. But it should also be true that with hindsight, some war critics should rethink their criticism. The outcome the critics wanted — a long-term stable future for Iraq without the cost and trauma of international intervention — was as much a fantasy as hopes for a swift and easy transition to democracy.

Iraq was on its way to an explosion in 2002. The U.S.-led intervention brought that explosion forward in time, and exposed Americans and allies to the shrapnel wounds. But the intervention may also have accelerated Iraq’s post-Saddam stabilization — opening the way to internal reconciliation and Iraq’s return to the community of nations.

Critics of the Iraq war often compare it to Vietnam. I wonder if the better comparison is not Korea: a war that once looked like a pointless stalemate, but that gained a strategic rationale as South Korea grew into a wealthy democracy. I remember a conversation I had with an American officer when I visited Iraq in 2005.

“What do you hope to achieve here?” I asked. “I mean, you personally?”

He answered: “Someday I’d like to bring my kids to visit a successful Iraq and tell them, ‘I made this possible.’” It’s early yet for this officer to begin planning his return trip. But comparing Iraq today to Iraq then — that trip has come a lot closer.