Air strikes over Baghdad signalled the start of the US-led invasion of Iraq. President Bush said the invasion was undertaken because Saddam Hussein's government possessed weapons of mass destruction and supported terrorism. Within three weeks Baghdad had fallen and the country was under the control of US-led coalition.

Despite President Bush's declaration that major combat operations in Iraq had ended, attacks on coalition forces were developing into a fully fledged insurgency. Law and order had never been fully restored after Saddam Hussein's defeat. Much of the initial violence was led by Sunni fighters, opposed to the invasion and the establishment of a new government.

The US-led coalition returned sovereignty to Iraq, allowing the appointed interim Prime Minister Iyad Allawi to assume power. A cabinet was also sworn into office. The establishment of a new government was conducted in the face of mounting resistance from insurgents and growing US casualties.

As the conflict continued, so the sophistication of insurgent attacks grew. Car bombs and improvised explosive devices placed at roadsides took an increasing toll on American soldiers.

Falluja, a stronghold of the Sunni insurgency west of Baghdad, was the scene of fierce fighting for several weeks at the end of 2004. The joint assault by the US and the Iraqi armies displaced most of the city's population and left many of its buildings destroyed.

Iraqi voters went to the polls to choose the 275 members of their new national assembly. The United Iraqi Alliance took the most votes, but fell short of a majority. In some Sunni areas turnout was as low as 2%. The new assembly was given the task of drawing up Iraq's constitution.

In October the number of dead American service personnel reached another landmark. Most of those killed were in their 20s. Roadside bombs and hostile fire were the two main causes of death, and the regions of Baghdad and Anbar accounted for over 50% of US casualties. In the same month Iraqi voters approved a new constitution which aspired to set up an Islamic federal democracy.

Provisional figures gave the Shia-led United Iraqi Alliance a victory in Iraq's first elections since Saddam Hussein was removed from power.

Texan Dustin R. Donica became the 3,000th US soldier to die in Iraq. He was killed by small arms fire in Baghdad. His death came as President Bush considered increasing American troop levels, with the aim of stabilising an increasingly bloody situation.

The US launched a joint US-Iraqi offensive aimed at restoring security in Baghdad in February. Extra troops were sent to the area in and around the capital as part of the security drive, or surge, which followed escalating violence.

The radical Shia cleric Moqtada Sadr announces a freeze on the activities of his Mehdi Army militia for six months.

Top US commander Gen David Petraeus says the troop surge has coincided with a "remarkable" improvement in security in Iraq. The plan is to begin reducing US troop numbers by about 20,000 by July 2008. Any further reduction in numbers will depend on conditions on the ground.