BAGHDAD, Iraq. More than two decades after American tanks rolled across the Kuwaiti border to topple Saddam Hussein, the United States has completed the withdrawal of its military forces from Iraq. The departure marks the formal close of one of the most consequential and costly interventions in modern American foreign policy, one that reshaped the Middle East, cost hundreds of thousands of lives, and left Iraq more vulnerable than ever to the influence of its powerful neighbor, Iran.

The withdrawal does not end America's relationship with Iraq, but it does draw a symbolic line under a war that began in March 2003 with the promise of swift regime change and democratic transformation. Instead, it produced years of insurgency, sectarian slaughter, and a fragile state that has struggled to stand fully on its own.

A War Built on a Faulty Premise

The invasion was launched on the claim that Saddam Hussein's government possessed weapons of mass destruction, a justification that later proved unfounded. What followed was not the quick, welcomed liberation that American planners had anticipated, but a prolonged and bloody occupation. One of the earliest and most consequential missteps came almost immediately: American administrators disbanded the Iraqi army, instantly creating a vast pool of trained, armed, and now unemployed men with every incentive to join an emerging insurgency.

Sunni militants, many of them former Saddam loyalists, turned against both the Shia majority and the American and British forces occupying the country. Al-Qaeda, which had little presence in Iraq before the invasion, poured fighters and resources into the chaos, seizing the opportunity to strike at American forces and stoke a wave of anti-American sentiment across the Arab world. Suicide bombings targeted United Nations headquarters, hotels, police stations, and ordinary Iraqis accused of collaborating with occupying forces. By the end of 2003, some 300 American soldiers had died, even though President George W. Bush had already declared major combat operations over.

Elections, Sectarian Fracture, and the Rise of Iranian-Aligned Power

Iraq's first democratic elections brought a complicated reckoning. Twelve different political groupings competed, but a boycott by most Sunni Muslims handed a dominant position to the Shia majority, which had endured decades of oppression under Saddam. That imbalance sowed the seeds of future conflict. Years later, Shia Prime Minister Nouri al-Maliki would accuse his Sunni vice president of organizing terrorist attacks, prompting the vice president's flight into Kurdish territory and a renewed wave of sectarian bombings that killed hundreds.

President Bush's 2007 troop surge, which brought American force levels to 150,000, temporarily suppressed the violence enough that troops were pulled from Baghdad's streets in 2009. But the calm proved fragile. Violence soon crept back, and it was not until Iraqi security forces, trained by the Americans, gained ground that civilian deaths fell to their lowest levels since the invasion.

In December 2011, President Barack Obama formally declared the war over and withdrew American troops into Kuwait, fulfilling a central campaign promise. Yet within weeks, the democratic state Washington had hoped to leave behind was already fracturing along the same sectarian lines that had never truly healed.

An Economy Hollowed Out, a Region Transformed

The human and institutional toll of the war extended well beyond the battlefield. Iraq's once self-sufficient agricultural economy, which in the 1980s produced wheat, rice, fruit, vegetables, and livestock for export, was devastated during the years of occupation. By 2010, oil exports accounted for roughly 95 percent of the country's revenue, leaving Iraq's economy dangerously exposed to volatile global markets and starved of the diversified industries it once had.

The invasion's shockwaves also reached far beyond Iraq's borders. It fueled a surge in global terrorism, with al-Qaeda-linked attacks striking Bali, Jakarta, and Istanbul, and it accelerated the growth of militant networks with cells as far afield as London, Poland, and the Czech Republic. Analysts have long argued that the war, rather than containing extremism, helped incubate it.

Iran's Enduring Shadow

Perhaps the most lasting irony of the American invasion is that it removed the one regional power capable of counterbalancing Iran, only to see Tehran's influence expand steadily in the vacuum left behind. Shia political parties and militias with close ties to Iran gained outsized influence in Baghdad's postwar order, a dynamic that has persisted through successive Iraqi governments. Even as American troops now depart for good, Iranian-backed factions remain deeply embedded in Iraq's security services, militias, and political institutions, a legacy that no amount of American military presence was able to reverse.

For Washington, the withdrawal closes a long and costly chapter, but it does not resolve the fundamental question that has hung over Iraq since 2003: whether a state assembled from competing sectarian and ethnic factions (Shia, Sunni, and Kurd) can hold together as a unified nation, or whether the country's future lies in some looser federal arrangement, or even partition. Two decades on, with Iranian influence entrenched and Iraq's economy still overwhelmingly dependent on oil, the answer remains as unsettled as it was in the war's chaotic aftermath.