As US President Donald Trump considers putting “boots on the ground” to topple the Iranian regime amid the US-Israel bombing campaign, it is worth recalling a different invasion from 20 years ago that profoundly reshaped the Middle East.The stated aim of the 2003 invasion of Iraq — led by the US and including troops from the UK, Australia, Denmark, the Netherlands and Poland — was to destroy its “weapons of mass destruction (WMDs)” and “liberate” its people from the rule of Saddam Hussein.Two decades on, Iraq continues to bear deep scars from that invasion — internecine conflict, insurgency, state fragmentation and the rise of extremist groups.The moment of regime change: What happened in Iraq in 2003?George W Bush assumed office in January 2001. After the September 11 attacks, his administration cited Iraq’s alleged possession of WMDs and purported links to terrorist groups, including Al-Qaeda, as grounds for military action. Those claims would later prove unfounded.In his 2002 State of the Union address, US President George W Bush said: “States like these and their terrorist allies constitute an axis of evil, arming to threaten the peace of the world…”By March 2003, Bush concluded that diplomatic efforts had failed and delivered an ultimatum to Saddam Hussein: Leave the country within 48 hours. Several countries including France, Germany and Russia objected to the move, seeing it as a build-up towards war.The Iraqi president refused to comply and US-led forces attacked Iraq on the morning of March 20. Within a couple of weeks, Baghdad had fallen. The toppling of Hussein’s statue in Firdos Square would become the most abiding image of the Iraq War. Hussein, who had fled, was caught in December 2003 after one of the biggest manhunts in history.Story continues below this adBush infamously declared: “Mission accomplished”. But the victory on the battlefield quickly gave way to a bigger challenge: How to govern a society that had for long been strung together through repression.Following the collapse of the Ba’athist regime, the major cities of Iraq erupted in violence and looting, mostly directed at government offices. Regional and sectarian conflicts broke out across the country over old grudges.An interim governing body — the Coalition Provisional Authority (CPA), headed by a senior American diplomat — was established. The primary objective of the interim government was to maintain security, law and order, and to rebuild Iraq’s severely damaged infrastructure.Its efforts, however, were largely hampered on account of rising insurgency involving both Iraqi and non-Iraqi fighters from other Arab states. The majority of them were the thousands of people who had been removed from the former ruling party and the Iraqi army. Faced with unemployment and disenfranchisement, they contributed to the acute lawlessness that followed.Story continues below this adAftermath of the 2003 Iraq invasionSectarian violence emerged as one of the most immediate and far-reaching consequences of the invasion. The removal of Hussein and the subsequent empowerment of the Shia majority resulted in violent backlash from the Sunnis who felt marginalised.The Shia-Sunni violence peaked in 2006 with the bombing of the Al-Askari mosque, a major Shia shrine, by Al-Qaeda. Many analysts consider it a watershed moment towards full-blown sectarian war. The resistance against foreign presence had swiftly intertwined with the battle over communal identity.Meanwhile, efforts to hand over power to the Iraqi people continued. In June 2004 the CPA was dissolved and political authority passed on to an interim government headed by Ghazi-al-Yawar.In January 2005, despite violence, elections were held successfully for Iraq’s new Transitional National Assembly.Story continues below this adIn April 2005, the role of Iraqi president was taken over by the Kurdish leader Jalal Talabani. A draft constitution was soon approved.But the predominant presence of the Shia and Kurdish communities in the new government further alienated Sunnis.The withdrawal of additional US troops in 2007 along with Sunni Awakening — a movement in which Sunni insurgents eventually moved away from extremism — did reduce violence to some extent. Political reconciliation, however, remained a distant dream.The withdrawal of US troops and rise of ISISIn December 2011, the US military held a ceremony in Baghdad to formally declare an end to its mission in Iraq.Story continues below this adThe country’s internal challenges, however, were far from over.A new extremist threat emerged within the power vacuum left by the withdrawal of American forces — the Islamic State of Iraq and Syria (ISIS).Driven out of Iraq by the Sunni Awakening in 2007, the group made a powerful comeback in 2013, riding on mounting Sunni discontent.By 2014, ISIS had taken over Mosul and other key cities, and declared a caliphate of its own. It demanded that Muslims all over the world swear allegiance to its leader, Abu Bakr al-Baghdadi, and migrate to territory under its control.Story continues below this adBy the end of 2015, the group ruled over an area with a population of approximately 12 million people and enforced an extremist interpretation of Islamic law. It frequently deployed beheadings, crucifixions and mass shootings against its enemies.Despite several US-led airstrikes and other efforts to squash the group, ISIS remained rather resilient. It was only in March 2019 that the caliphate collapsed. Later that year, Baghdadi was killed.Despite losing control, the group continues to function.A 2020 report by Washington DC-based thinktank Wilson Center notes: “Since the Islamic State fell in Syria and the caliphate collapsed in March 2019, ISIS launched hundreds of attacks primarily in the central desert region, in the east near the Iraqi border and to a lesser extent in the south near the Jordanian border.”The structural weaknesses that led to its rise remain unresolved.Long-term effect: Death, displacement, political uncertaintyStory continues below this adAlthough numbers vary, a report published by the World Health Organisation in 2008 estimated 151,000 Iraqis to have died from violence between March 2003 and June 2006.Yet another population survey published in PLOS Medicine in 2013 suggested that between March 2003 and mid-2011, an approximate 405,000 excess deaths were attributed to the conflict.There was also the large-scale displacement caused by the conflict. As per reports, the number of internally displaced people rose from zero registered in 2003 to 2.6 million in 2007. With the rise and advance of the Islamic State in 2013, the number of internally displaced persons rose again, reaching a peak of 4.5 million in 2015. As of 2022, there were 1.2 million internally displaced people across the country.Millions of other Iraqis turned into refugees. As of 2022, the UN had registered 3,45,305 Iraqi refugees living mostly in Germany, Jordan and Iran.Story continues below this adIraq today is a federal parliamentary republic with elections having been held here regularly since 2005. Yet, its problems of endemic corruption, fragile governance and influence of militias in politics remain.Two decades after regime change, Iraq stands as both a cautionary tale and a living polity still striving for coherence amid competing forces.