Fallujah during the Iraq War

The United States bombardment of Fallujah began in April 2003, one month after the beginning of the invasion of Iraq. In April 2003 United States forces fired on a group of demonstrators who were protesting against the US presence. US forces alleged they were fired at first, whereas residents instead claimed that US forces fired indiscriminately at the crowd without provocation. 17 people were killed and 70 were wounded. In a later incident, US soldiers fired on protesters again; Fallujah's mayor, Taha Bedaiwi al-Alwani, said that two people were killed and 14 wounded. Iraqi insurgents were able to claim the city a year later, before they were ousted by a siege and two assaults by US forces. These events caused widespread destruction and a humanitarian crisis in the city and surrounding areas. As of 2004, the city was largely ruined, with 60% of buildings damaged or destroyed, and the population at 30%–50% of pre-war levels.

Although the majority of the residents were Sunni and had supported Saddam Hussein's rule, Fallujah lacked military presence just after his fall. There was little looting and the new mayor of the city—Taha Bidaywi Hamed, selected by local tribal leaders—was pro-United States. When the U.S. Army's 1st Battalion / 2nd Brigade 82nd Airborne entered the town on April 23, 2003, they positioned themselves at the vacated Ba'ath Party headquarters, a local school house, and the Ba'ath party resort just outside town (Dreamland)—the US bases inside the town erased some goodwill, especially when many in the city had been hoping the US Army would stay outside of the relatively calm city.

On the evening of April 28, 2003, several hundred residents defied the US curfew and marched down the streets of Fallujah, past the soldiers positioned in the former Ba'ath party headquarters, to protest the military presence inside the local school. US soldiers fired upon the crowd, killing as many as 17 and wounding more than 70 of the protesters. US soldiers alleged that they were returning fire, but protesters stated they were unarmed. Independent observers from a human rights group found no evidence that US forces had come under attack. The US suffered no casualties from the incident.

Two days later, on April 30, the 82nd Airborne was replaced in the city by Fox Troop from 2nd squadron of the / U.S. 3rd Armored Cavalry Regiment. The 3rd Cavalry was significantly smaller in number and chose not to occupy the same schoolhouse where the shooting had occurred two days earlier. On the same day soldiers shot three protesters in front of U.S. Forward Operating Base "Laurie," established in the former Ba'ath party headquarters, and next to the Mayor's office. At this point in time the 3rd Cavalry controlled all of Al Anbar province, and it became evident a larger force was needed. The now battalion-sized element of the 3rd Cavalry (2nd squadron) in Fallujah was replaced by the 2nd Brigade of the 3rd Infantry Division.^{[citation needed]}

During the summer, the US Army decided to close down its last remaining base inside the city (the Ba'ath party headquarters; FOB Laurie). At this point the 3rd ACR had all of its forces stationed outside Fallujah in the former Baathist resort, Dreamland. After the May 11 disarmament of the Mujahedin-e-Khalq and subsequent protected persons assignment under the Fourth Geneva Convention, the incoming 3rd Infantry Division also began using the large MEK compound adjacent to Dreamland to accommodate its larger troop presence in Fallujah. Under its control, the 3rd Infantry Division maintained no bases inside the city of Fallujah.

On 30 June a "huge explosion" occurred in a mosque in which the imam, Sheikh Laith Khalil, and eight other people were killed. Residents of the city stated the army fired a missile at the mosque, while U.S. Colonel Joseph Disalvo stated that the explosion took place in a building adjacent to the mosque. Just a couple of days earlier things had been much quieter, although US troops had been confiscating motorbikes as a preventive measure against terrorist attacks.

Two months after the 3rd Infantry took control of Fallujah from the 3rd Cavalry, it was redeployed home. The 3rd Cavalry again assumed control of Fallujah with only one squadron. Attached to that Squadron was the 115th MP Company from the Rhode Island Army National Guard. The 115th MPs made routine patrols and frequent house raids searching for insurgents and weapons caches. In September 2003, the 3rd Brigade of the 82nd Airborne was deployed to replace the 3rd Cavalry in Ramadi and Fallujah. The 3rd Cavalry was then left to control all of the al-Anbar province except for these two cities.

Approximately one year after the invasion, the city's Iraqi police and Iraqi Civil Defense Corps were unable to establish order. Insurgents launched many attacks, some on police stations in the city, killing at least 20 police officers. Beginning in early March 2004, the Army's 82nd Airborne Division commanded by Major-General Charles H. Swannack Jr. gave a transfer of authority of the al-Anbar province to the I Marine Expeditionary Force commanded by Lt. General Conway. The 3rd Cavalry and the 3rd Brigade of the 82nd Airborne were then sent home.