Iraq's invasion of Kuwait in 1990 ended in Iraq's defeat by a U.S.-led coalition in the Persian Gulf War (1990–91). However, the Iraqi branch of the Baʿth Party, headed by Ṣaddām Ḥussein, managed to retain power by harshly suppressing uprisings of the country's minority Kurds (Kurd) and its majority Shīʿite Arabs. To stem the exodus of Kurds from Iraq, the allies established a “safe haven” in northern Iraq's predominantly Kurdish regions, and allied warplanes patrolled “no-fly” zones in northern and southern Iraq that were off-limits to Iraqi aircraft. Moreover, to restrain future Iraqi aggression, the United Nations (UN) implemented economic sanctions (sanction) against Iraq in order to, among other things, hinder the progress of its most lethal arms programs, including those for the development of nuclear, biological, and chemical weapons (weapon of mass destruction). (See weapon of mass destruction.) UN inspections during the mid-1990s uncovered a variety of proscribed weapons and prohibited technology throughout Iraq. That country's continued flouting of the UN weapons ban and its repeated interference with the inspections frustrated the international community and led U.S. Pres. Bill Clinton (Clinton, Bill) in 1998 to order the bombing of several Iraqi military installations (code-named Operation Desert Fox). After the bombing, however, Iraq refused to allow inspectors to reenter the country, and during the next several years the economic sanctions slowly began to erode as neighbouring countries sought to reopen trade with Iraq.

In central Iraq units of the Republican Guard—a heavily armed paramilitary group connected with the ruling party—were deployed to defend the capital of Baghdad. As U.S. Army and Marine forces advanced northwestward up the Tigris-Euphrates river valley, they bypassed many populated areas where Fedayeen resistance was strongest and were slowed only on March 25 when inclement weather and an extended supply line briefly forced them to halt their advance within 60 miles (95 km) of Baghdad. During the pause, U.S. aircraft inflicted heavy damage on Republican Guard units around the capital. U.S. forces resumed their advance within a week, and on April 4 they took control of Baghdad's international airport. Iraqi resistance, though at times vigorous, was highly disorganized, and over the next several days army and Marine Corps units staged raids into the heart of the city. On April 9 resistance in Baghdad collapsed, and U.S. soldiers took control of the city.

After 35 years of Baʿthist rule that included three major wars and a dozen years of economic sanctions, the economy was in shambles and only slowly began to recover. Moreover, the country remained saddled with a ponderous debt that vastly exceeded its annual gross domestic product, and oil production—the country's single greatest source of revenue—was badly hobbled. The continuing guerrilla assaults on occupying forces and leaders of the new Iraqi government in the years after the war only compounded the difficulty of rebuilding Iraq.

In the Shīʿite regions of southern Iraq, many of the local religious leaders (ayatollahs) who had fled Ṣaddām's regime returned to the country, and Shīʿites from throughout the world were able to resume the pilgrimage to the holy cities of Al-Najaf and Karbalāʾ that had been banned under Ṣaddām. Throughout the country Iraqis began the painful task of seeking loved ones who had fallen victim to the former regime; mass graves, the result of numerous government pogroms over the years, yielded thousands of victims. The sectarian violence that engulfed the country caused enormous chaos, with brutal killings by rival Shīʿite and Sunni militias. One such Shīʿite militia group, the Mahdi Army, formed by cleric Muqtada al-Sadr (Ṣadr, Muqtadā al-) in the summer of 2003, was particularly deadly in its battle against Sunnis and U.S. and Iraqi forces and was considered a major destabilizing force in the country.

Unlike the common consent reached in the Persian Gulf War, no broad coalition was assembled to remove Ṣaddām and his Baʿth Party from power. Although some European leaders voiced their conditional support for the war and none regretted the end of the violent Baʿthist regime, public opinion in Europe and the Middle East was overwhelmingly against the war. Many in the Middle East saw it as a new brand of anti-Arab and anti-Islamic imperialism, and most Arab leaders decried the occupation of a fellow Arab country by foreign troops. Reaction to the war was mixed in the United States. Though several antiwar protests occurred in American cities in the lead-up to the invasion, many opinion polls showed considerable support for military action against Iraq before and during the war. Surprisingly, American opinions on the war sometimes crossed traditional party lines and doctrinal affiliation, with many to the right of the avowedly conservative Bush seeing the war as an act of reckless internationalism and some to the political left—appalled by the Baʿthist regime's brutal human rights violations and its consistent aggression—giving grudging support to military action.

As violence continued and casualties mounted, however, more Americans (including some who had initially supported the war) began to criticize the Bush administration for what they perceived to be the mishandling of the occupation of Iraq. The appearance in the news of photographs of U.S. soldiers abusing Iraqis at Abu Ghraib prison west of Baghdad—a facility notorious for brutality under the Baʿth regime—further damaged world opinion of the United States. In addition, a U.S. bipartisan commission formed to investigate the September 11 attacks reported in July 2004 that there was no evidence of a “collaborative operational relationship” between the Baʿthist government and al-Qaeda (Qaeda, al-)—a direct contradiction to one of the U.S. government's main justifications for the war.