The invasion of Iraq began on March 20, 2003, with the same combination of air power and precision that had worked in Afghanistan. But this was fundamentally different. This was not a war against a government harboring terrorists. This was an invasion to overthrow a sovereign government, topple its president, and remake its political system.

The decision to invade Iraq remains one of the most consequential and contested decisions in American history. The stated rationale was that Iraq possessed weapons of mass destruction and posed an immediate threat to the United States. The intelligence was wrong. No WMDs were ever found. But in March 2003, the decision had been made, Congress had authorized military action, and the invasion began.

The military campaign was fast. The U.S. deployed more than 300,000 troops, organized around 3rd Infantry Division (Mechanized), 1st Marine Expeditionary Force, and supporting units from Britain, Poland, Australia, and other coalition partners. The plan was to rapidly move from Kuwait northward into Iraq, destroy the Iraqi military, and take control of Baghdad.

The Iraqi military, what remained of it after twelve years of sanctions and no-fly zones, was no match for the American military. The Republican Guards, Saddam's elite units, were neither well-equipped nor well-led compared to American forces. The invasion moved faster than the military planners had anticipated.

The most dramatic moment came in early April, with what became known as "Thunder Run." Colonel David Perkins of the 3rd Infantry Division ordered his brigade to make a rapid armored assault down Highway 8 directly into Baghdad. It was unorthodox—a dramatic cavalry charge through a major city with a brigade-sized force, supported by air power and helicopters. Perkins believed that speed and shock could overwhelm the Iraqi defenders, and he was right.

The Thunder Run succeeded beyond expectations. The Iraqi defenders were surprised, confused, and quickly overwhelmed. American forces established a presence on the streets of Baghdad. The psychological impact was enormous: the American military was inside the capital.

On April 9, 2003, nineteen days into the invasion, the most iconic image of the war was created: the toppling of the statue of Saddam Hussein in Firdos Square. American Marines and Iraqi civilians pulled the statue down, smashing it with sledgehammers and dragging it through the streets. For those watching at home, it seemed to symbolize the end of an era. The tyrant was gone. The war was won.

President Bush, in a speech aboard the USS Abraham Lincoln on May 1, declared "Mission Accomplished." The banner behind him became instantly infamous.

From a purely military perspective, the invasion was a triumph. The U.S. military had invaded a country, destroyed its army, toppled its government, and taken control of its capital in less than three weeks with remarkably low casualties. Fewer than 200 American military deaths. The blitzkrieg had worked.

But the mission was not accomplished. It was, in fact, just beginning. The problems that would consume the next eighteen years of war were already visible to anyone willing to look:

The looting and collapse of Iraqi state institutions. No plan for what came after military victory. The disbanding of the Iraqi Army and removal of Baathist party members from government. The creation of a security vacuum that would be filled by insurgent groups. The alienation of the Sunni population. The potential for sectarian conflict.

Within weeks, American forces in Baghdad were facing ambushes, IED attacks, and organized resistance. The military victory was complete, but the political objective—a stable, democratic Iraq—was already slipping away. And the true costs of the decision to invade Iraq, in American lives, Iraqi lives, and international credibility, were only beginning.