2003: Fall of Saddam
The US and British invasion begins with dawn air strikes on March 20, 2003, after then-US president George W. Bush accuses Saddam of holding "weapons of mass destruction".
By April 9, US forces have taken central Baghdad, where a large statue of the Iraqi dictator is toppled.
Bush announces the end of major combat operations on May 1 aboard the USS Abraham Lincoln aircraft carrier in the Gulf under a banner that reads "Mission Accomplished".
But by October, Washington admits it has found no weapons of mass destruction.
Saddam is captured hiding near his home town of Tikrit in December. He is hanged three years later.
2004: Transfer of power
The US-led administration hands political power back to the Iraqis in June 2004, two months after images of torture and abuse of Iraqi prisoners at the Abu Ghraib US military prison shock the world.
The following year, the country votes in its first multi-party election in half a century, a poll boycotted by the Sunni Muslim minority to which Saddam belonged.
A 2005 constitution enshrines autonomy for the Iraqi Kurdistan region in the north.
2006: Sectarian conflict flares
In February 2006, Al-Qaeda-linked jihadists blow up one of the country's main Shia shrines in Samarra, sparking a wave of sectarian killings which leaves tens of thousands dead and lasts until 2008.
In August 2007, more than 400 people die in the deadliest attacks in four years, against the Yazidi minority in the north.
2011: US troops leave
The last US troops pull out on December 18, 2011, ending a near nine-year occupation and leaving behind a country mired in political crisis.
Between 2003 and 2011 more than 100,000 civilians have been killed, according to the Iraq Body Count database. The US lost nearly 4,500 Americans.
2014: Islamic State offensive
The Islamic State of Iraq and the Levant (ISIL), later rebranded the Islamic State (IS), captures the city of Fallujah and parts of Ramadi in a lightning offensive in January 2014.
In June, they seize second city Mosul and by the end of the year the group holds one-third of the oil-rich country.
After Baghdad appeals for help, a US-led coalition helps drive IS from the northern cities, with victory declared at the end of 2017.
2018: Elections and stalemate
Firebrand pro-Iranian Shia cleric Moqtada Sadr, whose militia battled US troops after the invasion, wins a surprise victory in legislative elections in May 2018.
But the ensuing talks to form a new parliament with other blocs lead to four months of political paralysis.
In October, the moderate Kurd Barham Saleh becomes president after a parliamentary vote and instructs former vice president Adel Abdel Mahdi to form a government.
2019: Bloody protests
Youth-led protests break out against corruption, unemployment and poor public services in October 2019.
Nearly 600 people die and 30,000 are injured as the rallies are bloodily put down. Dozens of activists have been killed or kidnapped since.
2020: Soleimani assassination
Top Iranian commander Qassem Soleimani is killed in Baghdad in a US drone strike on January 3, 2020, ordered by then-president Donald Trump, sending tensions soaring.
Five days later, Iran retaliates by firing missiles at military bases in Iraq housing US troops.
In April, Mustafa al-Kadhemi, who is well connected both in Tehran and Washington, becomes premier after two others fail to form a government.
2021: US combat mission over
With Kadhemi at his side, US President Joe Biden declares an end to the US "combat mission" in Iraq and says he wants a "new phase" of military cooperation.
Parliamentary elections are brought forward by a year to appease the popular protest movement that began in 2019.