The U.S.-led Coalition forces toppled the government and captured the key cities of a large nation in only 26 days.
The invasion did require a large army build-up like the 1991 Gulf War, but many did not see combat and many were withdrawn after the invasion ended.
This proved to be short-sighted, however, due to the requirement for a much larger force to combat the irregular Iraqi forces in the Iraqi insurgency.
General Eric Shinseki, U.S. Army Chief of Staff, recommended "several hundred thousand" troops be used to maintain post-war order, but then Secretary of Defense Donald Rumsfeld—and especially his deputy, civilian Paul Wolfowitz—strongly disagreed.
General Abizaid later said General Shinseki had been right.

The Iraqi army, armed mainly with older Soviet and Eastern European built equipment, was overall ill-equipped in comparison to the American and British forces.
Attacks on U.S. supply routes by Fedayeen militiamen were repulsed.
The Iraqis' artillery proved largely ineffective, and they were unable to mobilize their air force to attempt a defense.
The Iraqi T-72 tanks, the most powerful armored vehicles in the Iraqi army, were both outdated and ill-maintained, and when they were mobilized they were rapidly destroyed, thanks in part to the Coalition air supremacy.
The U.S. Air Force, Marine Corps and Naval Aviation, and British Royal Air Force operated with impunity throughout the country, pinpointing heavily defended resistance targets and destroying them before ground troops arrived.
The main battle tanks of the U.S. and UK forces, the U.S. M1 Abrams and British Challenger 2, functioned well in the rapid advance across the country.
Despite the many RPG attacks by irregular Iraqi forces, few U.S. and UK tanks were lost, and no tank crew-members were killed by hostile fire, although nearly 40 M1 Abrams were damaged in the attacks.
The only tank loss sustained by the British Army was a Challenger 2 of the Queen's Royal Lancers that was hit by another Challenger 2, killing two crew members.

The Iraqi army suffered from poor morale, even amongst the elite Republican Guard.
Entire units disbanded into the crowds upon the approach of invading troops, or actually sought out U.S. and UK forces to surrender to.
Many Iraqi commanding officers were bribed by the CIA or coerced into surrendering.
The leadership of the Iraqi army was incompetent – reports state that Qusay Hussein, charged with the defense of Baghdad, dramatically shifted the positions of the two main divisions protecting Baghdad several times in the days before the arrival of U.S. forces, and as a result the units were confused, and further demoralized when U.S. forces attacked.
The invasion force did not see the entire Iraqi military thrown against it; U.S. and UK units had orders to move to and seize objective target points rather than seek to engage Iraqi units.
This resulted in most regular Iraqi military units emerging from the war without having been engaged, and fully intact, especially in southern Iraq.
It is assumed that most units disintegrated to return to their homes.

According to the declassified Pentagon report, "The largest contributing factor to the complete defeat of Iraq's military forces was the continued interference by Saddam."
The report, designed to help U.S. officials understand in hindsight how Saddam and his military commanders prepared for and fought the invasion, paints a picture of an Iraqi government blind to the threat it faced, hampered by Saddam's inept military leadership and deceived by its own propaganda and inability to believe an invasion was imminent without further Iraqi provocation.
According to the BBC, the report portrays Saddam Hussein as "chronically out of touch with reality – preoccupied with the prevention of domestic unrest and with the threat posed by Iran."
The U.S.-led Coalition forces toppled the government and captured the key cities of a large nation in only 26 days. The invasion did require a large army build-up like the 1991 Gulf War, but many did not see combat and many were withdrawn after the invasion ended. This proved to be short-sighted, however, due to the requirement for a much larger force to combat the irregular Iraqi forces in the Iraqi insurgency. General Eric Shinseki, U.S. Army Chief of Staff, recommended "several hundred thousand" troops be used to maintain post-war order, but then Secretary of Defense Donald Rumsfeld—and especially his deputy, civilian Paul Wolfowitz—strongly disagreed. General Abizaid later said General Shinseki had been right.
The Iraqi army, armed mainly with older Soviet and Eastern European built equipment, was overall ill-equipped in comparison to the American and British forces. Attacks on U.S. supply routes by Fedayeen militiamen were repulsed. The Iraqis' artillery proved largely ineffective, and they were unable to mobilize their air force to attempt a defense. The Iraqi T-72 tanks, the most powerful armored vehicles in the Iraqi army, were both outdated and ill-maintained, and when they were mobilized they were rapidly destroyed, thanks in part to the Coalition air supremacy. The U.S. Air Force, Marine Corps and Naval Aviation, and British Royal Air Force operated with impunity throughout the country, pinpointing heavily defended resistance targets and destroying them before ground troops arrived. The main battle tanks of the U.S. and UK forces, the U.S. M1 Abrams and British Challenger 2, functioned well in the rapid advance across the country. Despite the many RPG attacks by irregular Iraqi forces, few U.S. and UK tanks were lost, and no tank crew-members were killed by hostile fire, although nearly 40 M1 Abrams were damaged in the attacks. The only tank loss sustained by the British Army was a Challenger 2 of the Queen's Royal Lancers that was hit by another Challenger 2, killing two crew members.
The Iraqi army suffered from poor morale, even amongst the elite Republican Guard. Entire units disbanded into the crowds upon the approach of invading troops, or actually sought out U.S. and UK forces to surrender to. Many Iraqi commanding officers were bribed by the CIA or coerced into surrendering. The leadership of the Iraqi army was incompetent – reports state that Qusay Hussein, charged with the defense of Baghdad, dramatically shifted the positions of the two main divisions protecting Baghdad several times in the days before the arrival of U.S. forces, and as a result the units were confused, and further demoralized when U.S. forces attacked. The invasion force did not see the entire Iraqi military thrown against it; U.S. and UK units had orders to move to and seize objective target points rather than seek to engage Iraqi units. This resulted in most regular Iraqi military units emerging from the war without having been engaged, and fully intact, especially in southern Iraq. It is assumed that most units disintegrated to return to their homes.
According to the declassified Pentagon report, "The largest contributing factor to the complete defeat of Iraq's military forces was the continued interference by Saddam." The report, designed to help U.S. officials understand in hindsight how Saddam and his military commanders prepared for and fought the invasion, paints a picture of an Iraqi government blind to the threat it faced, hampered by Saddam's inept military leadership and deceived by its own propaganda and inability to believe an invasion was imminent without further Iraqi provocation. According to the BBC, the report portrays Saddam Hussein as "chronically out of touch with reality – preoccupied with the prevention of domestic unrest and with the threat posed by Iran."
2003 invasion of Iraq