However fierce the fighting on the ground turns out to be, another war is under way that may end up being just as important to the ultimate outcome of a conflict in Iraq: the war of perceptions.
Whether the war is seen as one of liberation and international security, or of imperialist occupation and part of a crusade against Islam, will go a long way in shaping global security, international relations, and perceptions of the US for years to come.
For President Bush, this is the first war of the 21st century. Rather than a defensive fight against a declared foe typical of past wars, this one is against a gathering threat. But it is as much about winning the world over to a way of perceiving global security as it is about disarmament or regime change.
In the short term, this war of perceptions will determine which side in the long diplomatic debate over Iraq is judged to have been right. Long term, it could reverse - or cement - America's deteriorating image around the globe, with heavy implications for the war on terrorism
Depending on the way the Islamic world and Arab countries in particular react, the threat of a "clash of civilizations" that has lingered since the Sept. 11 attacks could either dissipate - or find new life.
"Earlier wars were state against state. The connection between one side and the people of the other or the rest of the world was largely nonexistent - but that has changed," says David Davenport, a diplomacy and foreign policy analyst at the Hoover Institution in Stanford, Calif.
A number of benchmarks will be key in determining the outcome of this battle of perceptions, experts say:
• Casualties, especially among Iraq's civilian and Muslim population, which could enrage Arab populations. Heavy casualties among US forces, meanwhile, could erode US support for the war.
• Chemical and biological weapons. First, whether or not Saddam Hussein uses them; and then, whether or not large caches of them are discovered. Either one could bolster the perception that Hussein is as dangerous as the US has claimed.
• Iraq's oil wealth. In the short term, whether or not Hussein torches oil wells, which would fuel his negative image in the world; and longer term, how Iraq's vast oil wealth is administered - in other words, how the antiwar argument that this is a war about oil stands up.
• The length of the war. A short war would bolster support for the American intervention. But some critics of the Bush doctrine of preventative war fear that "success" in Iraq would encourage the US to resort more quickly to the use of force in other conflicts.
• The Iraqi population's response to an American invasion.
"No one factor will determine how this war is viewed and what its long-term impact will be. It will be a cumulative effect from many things happening at once," says Patrick Clawson, deputy director of the Washington Institute for Near East Policy.
"If the war doesn't go well, casualties are high, and the US doesn't come up with [the] large stores of weapons of mass destruction it has said are there, perceptions [will] turn against the US. But if the war ends quickly, with WMDs found and a connection to terrorist organizations on top of that, and the Iraqi people show enthusiasm for working with the Americans on building a democracy, then the cumulative impact [will be] very different."
One challenge for the US is that negative opinion around much of the globe - and the fact the US is seen as having lost the battle of persuasion at the United Nations - means it starts with a deep deficit to make up, experts say.
"The Bush administration has done such a terrible job of explaining why this has to be done, they've flitted around from one reason to another, [so] it's going to take a while to chip away the skepticism no matter what happens," says Richard Stoll, a foreign-policy expert at Rice University in Houston.
"What happens in Iraq may be less important in the court of world opinion than how we got there," adds Mr. Davenport.
Such thinking is even stronger around the world, especially in the war region. "It doesn't matter what [the Americans] do," says Taher Masri, a former prime minister of Jordan. "The American insistence to go to war without the support of the [UN] Security Council, the firepower they will use against the Iraqi people, and the long-range effect of such a war make us terribly worried. They are opening a Pandora's box." Even as the United States claims that some 30 countries and counting are part of its "coalition of the willing," global surveys continue to show negative and even deteriorating perceptions of the US.
In a new nine-country poll by the Pew Research Center in Washington, "positive" views of the US sank to 12 percent in Turkey and to 48 percent in Britain.
But the Pew survey also found something else: an open-mindedness about what good might come from disarming Iraq and removing Saddam Hussein from power, even in strongly antiwar countries like Germany. "Success in these areas will go part of the way in repairing relations and addressing the very low image numbers," says Pew director Andrew Kohut, "but the way the US dealt with the UN is still going to keep the world focused on the way the US wields its power."
Early signals are already emerging of how what happens on the battlefield might affect shifting perceptions of the war. For example, France, which blocked UN authorization, now says it could join the fight if Hussein uses chemical weapons.
But even more than in Europe the US is clearly set on altering perceptions in the Middle East - a challenging job.
One of the first campaigns of the war will be for the southern city of Basra, where military officials have said they hope to beam images of cheering crowds to the watching world. Scenes of success will undermine Iraqi troops, the officials say, bolster the US and Britain against any later pitfalls, and defuse international criticism.
That may work in other regions, but it won't fly in the Middle East, says Cairo Times publisher Hisham Kassem.
Mr. Kassem admits he thinks US involvement in regime change will ultimately be positive, but says his viewpoint is not common and describes a growing, media-driven anger at the US mission in Iraq. "The Egyptian media is controlled by the government, which is threatened by the idea of regime change," explains Kassem. "So the media has not in any way been friendly to this military offensive."
Syrian analyst Imad Fawzi Shueibi, a professor at Damascus University, says the anger stems from a feeling that the US is attacking the region, not just one country.
"We cannot speak about Iraq only," he says. "It is only a theater of operation. They are going to invade our people."
But just as the Pew poll finds a basis for the US to begin winning over world opinion, other Middle East analysts say openings exist in the Arab world as well. For one thing, says Mr. Clawson, sympathy is particularly low for Hussein. "A lot of people know a lot more today about Saddam Hussein, so the support you had [during the Gulf war] just isn't there."
For many observers, the intense feelings - and suspicions - about the US and its intentions mean the "winner" of the perceptions war won't be determined until well after the last bomb of the hot war falls.
"There will be huge relief in Iraq and the sense of a job well done if they get rid of Saddam Hussein," says Charles Tripp, an Iraqi-history expert at London's School of Oriental and African Studies. "But it doesn't mean that people will be grateful to America. That will largely depend on what happens in the months afterward."