Al Jazeera breaks down some of the war’s defining moments in the following timeline.
Building up to invasion
On September 24, UK Prime Minister Tony Blair told the House of Commons: “Of course there is no doubt that Iraq, the region and the whole world would be better off without Saddam.”
Hearing the intent behind those statements, hundreds of thousands of people around the world poured onto the streets to protest against a war in Iraq.
In November 2002, UN Security Council Resolution 1441 afforded Iraq “a final opportunity to comply with its disarmament obligations”.
Four days later, the Iraqi parliament voted to reject the UN resolution.
Bush sends Saddam an ultimatum
On March 17, 2003, Bush declared an end to diplomacy and gave Saddam and his sons an ultimatum to “leave Iraq within 48 hours”.
March 19, 2003
In a televised statement, George W Bush says coalition forces are in the “early stages of a military operation to disarm Iraq” from its purported WMDs and remove Saddam from power.
The first assaults on Baghdad begin shortly after the expiry of the 48-hour deadline for Saddam and his sons to leave Iraq.
March 20, 2003
Coalition forces at the Iraqi-Kuwait border begin their offensive from the Gulf to take Basra and the surrounding oilfields.
Wearing a military uniform, Saddam appears on Iraqi state television to condemn “the criminal junior Bush” and call on Iraqis to defend their country.
March 23, 2003
Military operations move into southern Iraq, coming up against Iraqi resistance in the Battle of Nasiriyah, which lasted till April 2.
Air raids across the country kept the defending Iraqi army in chaos and prevented effective resistance.
April 9, 2003
US forces roll into the Iraqi capital and Baghdad is occupied.
Saddam’s statue in the main square is pulled down in an iconic moment broadcast live around the world. Operations continue against smaller factions of the Iraqi army.
May 1, 2003
George W Bush declares an end to the invasion, marking the beginning of the military occupation.
Despite being a secular leader, Saddam’s dictatorship was viewed by the majority, which was Shia Muslim, as inherently sectarian. Many Shia Muslims were forced out of Iraq under his regime’s Sunni minority rule.
During the de-Baathification process, the CPA relied heavily on the expertise of exiled Iraqi Shia Muslims. This arguably resulted in personal bias and political score-settling becoming pervasive throughout the process.
De-Baathification gutted the civil service and disbanded the military, security and other organisations central to public order.
On December 13, US troops capture Saddam Hussein near his hometown of Tikrit.
A resistance effort against Western occupation forces in the country begins. Hundreds are reported killed in fighting during a US military siege of Falluja, an hour west of Baghdad, that began April 4.
In late April, photographs are unearthed of US troops abusing and humiliating Iraqi prisoners at Abu Ghraib prison in Baghdad, sparking an international outcry and a US senate probe of alleged abuses.
Meanwhile, images of gruesome violence in Iraq spread around the world via internet videos as the US claims that Jordanian-born Abu Musab al-Zarqawi’s armed group, which became al-Qaeda in Iraq in late 2004, has attracted more fighters.
In July, Saddam appears in court for the first time, facing charges including war crimes and genocide.
In the aftermath of the US invasion, the Iraqi unemployment rate reaches 70 percent in August.
On January 30, the first multi-party elections in 50 years are held amid stringent security measures. Jalal Talabani, a Kurdish politician, is sworn in as president.
Masoud Barzani becomes the regional president of the semi-autonomous Kurdistan Regional Government.
Voters accept a new constitution that aims to create an Islamic federal democracy. Iraqis vote for a government and parliament.
The United Iraqi Alliance – a Shia-led party – wins the parliamentary elections.
By April of 2006, al-Qaeda in Iraq was fighting both against the occupation and other Iraqi sects, leaving the country awash in blood.
On May 20, 2006, Nouri al-Maliki becomes Iraq’s first democratically elected prime minister.
A month after the elections, Abu Musab al-Zarqawi, leader of al-Qaeda in Iraq, is killed in a US air raid. Stepping up to fill the void at the top of al-Qaeda in Iraq is one of its founders – Abu Ayyub al-Masri.
In February 2006, the dome of the al-Askari Shia shrine in Samarra was destroyed in a bombing. Sunni fighters are largely blamed for the attack, escalating sectarian tensions into what quickly became known as the Iraqi civil war.
Fighters loyal to Shia cleric Muqtada al-Sadr target 40 Sunnis at checkpoints in Baghdad, and nearly two dozen people were killed in a car bombing in Sadr City, a Shia district in eastern Baghdad, killing 62 and injuring 114 on July 1.
In July, the deadliest month for attacks and bombings, nearly 3,500 Iraqis were killed, about 110 people a day.
‘”Death squads” and bombings killed thousands, with neighbourhoods in mixed cities like Baghdad adopting more sectarian identities as minorities left.
On the morning of the start of Eid al-Adha on December 30, 2006, Saddam Hussein is executed for crimes against humanity.
An escalation in rebel activity prompts President Bush to propose a surge of 21,500 additional troops into Iraq in January 2007.
The al-Askari shrine in Samarra is attacked again.
Suicide attacks hit the north of the country, targeting Yazidis and killing and injuring hundreds.
The Iraqi Accordance Front, the main Sunni political bloc, withdraws from cabinet following a dispute.
Britain hands over the security of Basra to Iraqi forces as the country pushes towards reducing the number of its troops in Iraq.
Violence continues to escalate despite a troop surge. In April the British defence secretary says the final withdrawal of troops has been postponed after clashes between Shia fighters and Iraqi security forces.
In March, the Iraqi army, supported from the air by the US-led coalition, attacked al-Sadr’s Mahdi army in Basra. Iraq’s PM Nuri al-Maliki vowed security forces would battle the Shia militia in Basra “to the end”.
In May, the government and armed fighters reach a ceasefire.
By the end of 2008, the total number of foreign troops in the country – including US soldiers – stands at just over 151,000.
In February 2009, new US President Barack Obama announces that the US combat mission in Iraq would end by August 31, 2010, and that the final withdrawal of all US forces would take place at the end of 2011.
In July, UK Prime Minister Tony Blair’s successor, Gordon Brown, orders an independent inquiry into the decisions that led the country to war.
Parliamentary elections are held in March and no coalition wins enough votes for a majority as Iraq’s neighbours anxiously eye the voting.
Iraq’s leading army official criticises the planned withdrawal of US troops, saying that Iraq may not be ready for the move. The last US combat brigade leaves Iraq in August, but 50,000 troops remain for training and advisory purposes.
In November, Jalal Talabani is appointed as president and Nouri al-Maliki as prime minister. Parliament approves a new government that includes the major factions.
In January, Muqtada al-Sadr returns to Iraq after years of self-imposed exile in Iran.
Thousands gather in Baghdad and northern Iraq, demanding improved services and an end to corruption, apparently inspired by the Arab Spring protests that have spread across the region.
By December, the US announces an end to combat operations.