As Iraqi units quickly overran the country, U.S. officials resolved to contest the occupation. If left unchallenged, U.S. officials feared, Hussein might continue his military advance into Saudi Arabia. They further reasoned that allowing Hussein to consolidate his hold on Kuwait would garner him enormous political prestige and economic wealth and destabilize the international order that was emerging in the post-Cold War era.

President Bush resolved that he would take necessary steps, up to and including military force, to reverse the Iraqi conquest of Kuwait. And his decision to contest Iraqi expansionism resulted in two strategic initiatives, one centering on deterrence and the second on military action.

First, under Operation Desert Shield, Bush positioned American soldiers in Saudi Arabia as a deterrent against any Iraqi military move into territory beyond occupied Kuwait. Second, in partnership with numerous allies, Bush amassed military forces along the borders of Iraq and Kuwait as pressure on Hussein to abandon Kuwait.

When Hussein refused to leave, the allied militaries launched Operation Desert Storm in January 1991, featuring about five weeks of punishing aerial assaults on Iraqi military, political, and communications targets followed by a ground invasion that liberated Kuwait from Iraqi control.

Bush then made the important and controversial decision to halt his forward advance after the liberation of Kuwait, resisting the temptation to occupy Iraq and depose Hussein. Bush reasoned that a march to Baghdad would fragment his international alliance, exceed the mandate authorized by the United Nations, incur unacceptable U.S. casualties, and lead to a costly, prolonged occupation.

The U.S. president also called for an insurrection against Hussein from within Iraq's Sunni elite, but this move backfired badly, as Kurds and Shiites rebelled instead, prompting a brutal Sunni repression that actually bolstered Hussein's domestic position and power.

As the postwar situation stabilized, Bush and his Oval Office successor William J. Clinton gradually imposed a multi-faceted containment policy against Iraq.

Under Operations Northern Watch and Southern Watch, they established "no-fly zones" over Iraqi territory north of the 36th parallel and south of the 31st (eventually 33rd) parallel, designed to protect Iraq's Kurdish and Shiite populations from military repression and to prevent Hussein from massing his army on his international borders.

U.S. leaders also persuaded the United Nations to maintain the international financial restrictions imposed during the Gulf War until Hussein complied with all U.N. resolutions, including one calling for Iraq to eliminate its weapons of mass destruction (WMD).

U.S. officials also promoted international inspections of Iraqi military and scientific facilities designed to ensure compliance with the disarmament expectations. Both U.S. presidents also used occasional military strikes to punish Iraq for violating the U.N. resolutions, challenging Western warplanes, or inhibiting arms inspections. They hoped essentially to keep Hussein's power in check until his capacity and inclination for trouble-making eroded.

The containment policy, which lasted until the U.S. invasion of Iraq in 2003, achieved its immediate goal. Although Hussein remained in power in Baghdad, he proved unable to provoke another regional conflict, attack his own Kurdish or Shiite peoples living under the protection of Western military aircraft, or down a single one of those aircraft. The Iraqi economy remained stressed.

By hindering international weapons inspections, Hussein stoked fear that he again was developing WMD, but in reality—as confirmed by Western arms inspectors after 2003—Iraq's WMD program remained dysfunctional and impotent.

These achievements notwithstanding, the containment policy had an uncertain long-term prognosis.

As time passed, the no-fly zones became politically problematic, as Hussein exploited the situation to bolster his domestic political authority and to win world sympathy for the civilian victims of Western airstrikes. Effective arms inspections ended in December 1998. Hussein blamed the suffering of his people on the economic sanctions (rather than his own non-compliance with U.N. resolutions), and such powers as France and Russia wavered in their commitment to enforce sanctions.

In 1998, the terrorist Osama bin Laden cited the U.S. assaults on Iraq from airbases in Saudi Arabia as one cause of his declaration of war against the United States. Clinton bolstered containment in 1998 by embracing the concept of "regime change"—meaning that he would favor the overthrow of Hussein—but even that step had limited ability to guarantee security interests.

Whether the enhanced containment policy would have worked remains a matter of speculation. In hindsight, however, one could reasonably conclude that the maintenance of the containment approach into the new century had a fair chance of preserving essential U.S. interests in the Middle East during Hussein's lifetime at a small fraction of the costs incurred in the alternative approach implemented by Clinton's successor in the Oval Office.

V. War and Reconstruction, 2003-2011

The fifth era of U.S. policy toward Iraq centered on war and reconstruction.

President George W. Bush, unnerved by the September 11, 2001 terrorist attacks on the United States, launched a military invasion of Iraq designed to destroy Saddam Hussein's brutal regime.

Insecurity stemming from the 9/11 assaults, which was compounded by a series of anthrax attacks inside the United States in late 2001, led Bush to reinterpret Saddam Hussein—given his legacy of military expansionism and his apparent efforts to restore his WMD capabilities—as a dire threat to American security.

Hawks such as Vice President Dick Cheney and Secretary of Defense Donald Rumsfeld encouraged this reinterpretation, gaining the president's ear at the expense of Secretary of State Colin Powell and other advisers who were reluctant to wage war. Shell-shocked by the terrorist attacks of late 2001, Congress and the American people gave the president wide latitude to pursue a policy in Iraq centered on ousting Hussein by any means including force.

For 18 months following the 9/11 attacks, the Bush administration gradually led the United States to the brink of war. Speeches by leading officials portrayed the Hussein regime as a mortal danger to the security of the United States and other countries by suggesting that Iraq would likely supply WMD to terrorist groups, with catastrophic consequences. Administration officials also argued that the containment policy launched in 1991 had faltered, enabling Hussein to restore his antebellum capacity to do harm to his neighbors and his own people.

The United States secured U.N. Security Council resolution 1441, which censured Iraqi behavior and warned of serious consequences if it remained defiant. (The United States later claimed that this resolution provided a legal basis for war, a claim that France and other powers disputed.)

The Bush administration openly doubted the assurances of U.N. officials, who hastily resumed arms inspections in Iraq in an effort to avert war, that Iraq was free of WMD. U.S. leaders also rebuffed the advice of other countries, including such allies as France and Germany, that war was unnecessary and improper.

The build-up to war climaxed in early 2003 when the United States invaded Iraq.

On March 17, the Bush Administration issued an ultimatum to Hussein to leave Iraq within 48 hours or face the wrath of the American military. When Hussein, as expected, defied the ultimatum, Bush ordered the Pentagon to attack Iraq on March 19.

Some 125,000 U.S. soldiers, bolstered by 20,000 British and 500 Australian troops, launched aerial and ground operations that quickly resulted in a military victory. In combat operations lasting some 500 hours, the invading forces defeated and scattered the Iraqi army of some 400,000 soldiers, occupied the country, and demolished its regime, at a cost of 139 U.S. and 33 British fatalities. [Read Origins on coalition fighting in the Iraq War]

The luster of the military victory over Hussein's forces would soon be tarnished by the Bush Administration's flawed policy for the postwar period.

For starters, the post-invasion discovery that Hussein had actually lacked WMD capability eroded U.S. credibility given the administration's emphasis on the WMD threat in the build-up to war.

News about the grotesque abuses of Iraqi detainees by U.S. soldiers at the Abu Ghraib prison further undermined the public image of the United States around the world. Domestic and foreign opponents of the original decision to invade Iraq rallied in criticism of U.S. policies.

The Bush administration also blundered in political decisions about the post-combat phase of the invasion.

In the rush to war, top Pentagon officials generally neglected initiatives in the State Department to plan for postwar occupation. Secretary of Defense Rumsfeld refused to increase the size of the U.S. occupation force, despite requests for more troops from top uniformed officers, and the occupation forces proved unable to stymie a wave of lawlessness and violence that destabilized the country in the weeks following the downfall of Hussein.

The Pentagon sent retired General Jay Garner to Baghdad to organize popular elections for a new government within 90 days, a mission that failed miserably.

In May 2003, President Bush belatedly established the Coalition Provisional Authority (CPA) under former Ambassador L. Paul Bremer in hope of stabilizing the country. But Bremer erred massively when he issued CPA Orders Number 1 and 2, which disbanded the Baath Party and dissolved the entire Iraqi government.

In that dual stroke, Bremer eliminated the viable prospect of using vestiges of the Iraqi administrative infrastructure to govern the country and lead it into a brighter future. Instead, the orders alienated the elite, including many who had shown no loyalty to Hussein, rendering them unemployed and without purpose and thus vulnerable to an emerging anti-U.S. armed insurgency.

Indeed, within months of the military victory over Hussein, the United States faced a debilitating insurgency across Iraq. The armed opposition seemed to have three distinct sources: Sunnis who had been tied to the Hussein regime; Shiite militias, like the Mahdi Army led by Muqtada al-Sadr, who sought to attain political influence in the post-Hussein era; and non-Iraqi Islamists who infiltrated Iraq in pursuit of the opportunity to bloody the American military.

By December 2003, suicide attacks, sniper fire, car bombs, and roadside bombs had killed some 300 U.S. soldiers, more than double the number who died in the initial invasion. The death toll among G.I.s soared past 1,000 by September 2004 and 3,000 by January 2007.

The annual costs to the U.S. Treasury also rose dramatically, from $51 billion in 2003 to $102 billion in 2006. The security situation worsened through 2006, when anti-U.S. attacks occurred at nearly double the frequency and lethality as in 2005.

As the insurgency mounted, the Bush Administration labored to build a democratic government in Iraq and made steady if halting progress.

The first breakthrough came in 2004, when the Bush administration abandoned its initial quest to build a new state on the foundation of Iraqi expatriates, notably Ahmad Chalabi, who had proved woefully inadequate to the challenge. In addition, recognizing that the dominance of the CPA generated political backlash, Bremer dissolved the authority in June 2004 and established a multi-ethnic Iraqi Transitional Government to preside over the establishment of a permanent government.

In January 2005, millions of Iraqis participated in a democratic election that established a 275-member Transitional National Assembly, which set out to write a permanent constitution. A second democratic election, held in December 2005 under the new constitution, established the permanent Council of Representatives (that replaced the Transitional National Assembly) and a coalition government.

The inherent clash between the growing insurgency and the quest to democratize Iraq came to a head in 2006. Domestic critics of the Bush administration—including a growing number of members of his own Republican Party—pressured the president to withdraw immediately from Iraq even if that step would result in complete collapse of the new government. Democrats captured majorities in both the House and Senate in the midterm elections of 2006 and in 2007 the new congressional leaders called for prompt demilitarization of the U.S. effort in Iraq.

President Bush resolved instead to escalate and reform the military mission in Iraq. In a strategic initiative known as the "surge," he increased the number of G.I.s in Iraq from 120,000 to 160,000 and he ordered them to reform their modes of operation from using overwhelming firepower (which caused collateral damage and negative political repercussions) to restraining firepower and engaging in political initiatives designed to gain goodwill.

U.S. forces also skillfully used diplomacy, persuasion, and financial aid to mobilize various Iraqi factions to fight against insurgent groups. By 2008, the surge seemed to succeed. The insurgency faltered and the military and political situations stabilized.

Taking office in January 2009, President Barack Obama gradually terminated the U.S. military presence in Iraq. He ended U.S. combat operations in Iraq in August 2010 and, consistent with a Status of Forces Agreement (SOFA) signed in 2008, he withdrew all combat forces from the country in December 2011.

Obama pledged to transfer responsibility for Iraq's future to the Iraqi people and to engage in regional diplomacy to ease external pressures on the country. By the end of the U.S. occupation, the war in Iraq had left nearly 4,500 U.S. soldiers dead and more than 30,000 wounded and had drained more than $1 trillion from the U.S. Treasury.

As U.S. forces departed the country in late 2011, Iraq's future remained precarious.

Sectarian violence spiked, killing at least 250 civilians within a month of the U.S. withdrawal.

The democratic foundations of the government teetered, as Prime Minister Nouri al-Maliki, a Shiite, took steps to solidify his influence over Sunni legislators and as Sunni Vice President Tariq al-Hashemi fled to Kurdistan to escape arrest for allegedly having ordered assassinations some years before.

Having endured 24 years of brutal rule by the Hussein regime, Iraq also bore scars of the U.S. invasion, including some 100,000 Iraqis killed and two million displaced in 2003-2011 alone and its financial and physical infrastructures badly stressed.

The Way Forward: Iraq and the United States in the Aftermath of War

The 2010s will mark a century since World War I, the global conflict that resulted in the construction of Iraq from the remnants of the Ottoman Empire and also stimulated the rise of the United States to great power status.

During that century, both the United States and Iraq grew in size and stature, the former as a global great power committed to projecting power in defense of national interests in every region, and the latter determined to achieve dominant regional power and influence.

U.S. policy toward Iraq shifted dramatically during that century, from its original posture of relying on Britain to stabilize Iraq on behalf of common Western interests.

World War II, the Cold War, and the decolonization of the British Empire unleashed international dynamics that compelled U.S. officials to shape polices toward Iraq ranging from cooperation and rapprochement to major conflict and two rounds of warfare.

U.S. policy became most complicated in the early 21st century, when President Bush ordered the invasion and occupation of Iraq in an attempt to rebuild the country on a democratic, peaceful, and progressive foundation.

While this latest effort to remake Iraq achieved certain markers of success, it also generated political problems and unanticipated consequences that sowed the seeds of future trouble. Developments still to unfold in the 2010s and after ultimately will reveal the wisdom and effectiveness of U.S. policy toward Iraq during the first century of the relationship.

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For more on the history of U.S.-Iraq relations by Peter Hahn, see his Missions Accomplished?: The United States and Iraq Since World War I (Oxford University Press, 2011).