While his regime fell in just three weeks on April 9, 2003, the country was plunged into a grave crisis that included the emergence of the Islamic State group.

Here is a timeline of major events since the invasion.

- 2003: fall of Saddam -

The US-led invasion is launched with dawn air strikes on March 20 and announced to the world soon afterwards by US president George W. Bush in a televised address.

As international forces race across the desert of southern Iraq towards the capital, Saddam flees.

By April 9 US forces have taken control of Baghdad, where a large statue of Saddam is symbolically toppled.

Bush announces the end of major combat operations on May 1 aboard the USS Abraham Lincoln aircraft carrier returning from the Gulf, a banner that reads "Mission Accomplished" behind him.

By October Washington admits, however, that it has found no weapons of mass destruction.

Saddam is captured in December after nine months on the run. He is dragged bearded and dishevelled out of a small underground hideout and hanged three years later.

- 2004-2011: transfer of power -

The US-led administration officially hands political power back to Iraq in June 2004 and in January the following year, it votes in its first multi-party election in half a century, a poll boycotted by Sunni Muslims.

A 2005 constitution enshrines autonomy for the autonomous Iraqi Kurdistan region in the north.

The broadcast in April 2004 of images of torture and other abuse of Iraqi prisoners at the Abu Ghraib US military prison shocks the world.

In February 2006 Al-Qaeda-linked jihadists blow up one of the country's main Shiite shrines, in Samarra, sparking a wave of sectarian killings which leaves tens of thousands dead and lasts until 2008.

International forces start scaling down with the last US troops departing on December 18, 2011, ending a nine-year occupation and leaving behind a country mired in political crisis.

More than 100,000 civilians were killed between 2003 and 2011, according to Iraq Body Count database. The United States lost nearly 4,500 troops.

- 2014: Islamic State emerges -

The Islamic State of Iraq and the Levant (ISIL) launches a lightning offensive, benefitting from the support of Saddam loyalists and the weakness of the new Iraqi security forces.

In January 2014 ISIL and its allies capture the city of Fallujah and parts of Ramadi. In June they seize second city Mosul and Sunni Arab areas bordering the Kurdistan region. Tens of thousands of Christians and Yazidis flee.

The group declares a caliphate across the territory it has seized in Iraq and Syria, and rebrands itself the Islamic State (IS).

By the end of 2014, it holds one-third of oil-rich Iraq.

- The fightback -

Following an appeal for help from the Iraqi government, US warplanes strike IS positions in northern Iraq in August 2014 and then form an international anti-IS coalition.

In March 2015 Iraq announces the "liberation" of Tikrit, Saddam's hometown, after nearly 10 months under IS rule. Ramadi and Fallujah are freed in 2016.

After a nine-month battle backed by US air power, Mosul is retaken in ruins in July 2017.

In December Prime Minister Haider al-Abadi declares the "end of the war" against the IS group.

- 2017: Kurdistan, a new crisis -

A referendum on independence is held in Iraqi Kurdistan in September 2017 in defiance of a furious Baghdad, even more put out when 93 percent of voters back independence.

The non-binding vote is ruled unconstitutional by Iraq's top court and in mid-October Baghdad sends in troops to seize disputed oil-rich regions that Iraqi Kurdistan had controlled.