In a ceremony held in Baghdad on December 15, 2011, the war that began in 2003 with the American-led invasion of Iraq officially comes to an end. But violence continued and in fact worsened over the subsequent years. The withdrawal of American troops had been a priority of President Barack Obama, but by the time he left office the United States would again be conducting military operations in Iraq.

Five days after the 9/11 attacks, President George W. Bush announced the “War on Terror,” an umbrella term for a series of preemptive military strikes meant to reduce the threat terrorism posed to the American homeland. The first such strike was the invasion of Afghanistan in October 2001, which began a war that continued for two decades.

Throughout 2002, the Bush Administration argued that Iraqi president Saddam Hussein was allied with terrorists and developing “weapons of mass destruction.” By all accounts, Hussein was responsible for many atrocities, but there was scant evidence that he was developing nuclear or chemical weapons. Behind closed doors, intelligence officials warned the case for war was based on conjecture—a British inquiry later revealed that one report’s description of Iraqi chemical weapons had actually come from the Michael Bay-directed action movie The Rock. The governments of the U.S. and the U.K., however, were resolute in their public assertions that Hussein posed a threat to their homelands, and went ahead with the invasion.

The invasion was an immediate success insofar as the coalition had toppled Hussein’s government and occupied most of Iraq by mid-April. What followed, however, was eight years of insurgency and sectarian violence. American expectations that Iraqis would “greet them as liberators” and quickly form a stable, pluralistic democracy proved wildly unrealistic. Though the coalition did install a new government, which took office in 2006, it never came close to pacifying the country. Guerilla attacks, suicide bombings and improvised explosive devices continued to take the lives of soldiers and civilians, and militias on both sides of the Sunni-Shia divide carried out ethnic cleansings.

The American public remained skeptical of the war, and many were horrified at reports of atrocities carried out by the military and CIA. Leaked photos proved that Americans had committed human rights abuses at the Abu Ghraib prison, and in 2007 American military contractors killed 17 civilians in Baghdad’s Nisour Square. Opposition to the war became an important talking point in Obama’s bid for the presidency.

On New Year’s Day 2009, shortly before Obama took office, the U.S. handed control of the Green Zone—the Baghdad district that served as coalition headquarters—to the Iraqi government. Congress formally ended its authorization for the war in November, and the last combat troops left the following month. Even by the lowest estimates, the Iraq War claimed over 100,000 lives; other estimates suggest that the number is several times greater, with over 205,000 civilian deaths alone.

Over the next three years, ongoing sectarian violence blossomed into a full-out civil war. Many of the militias formed during the Iraq War merged or partnered with extremist groups in neighboring Syria, itself experiencing a bloody civil war. By 2014 the Islamic State of Iraq and the Levant, which absorbed many of these groups, controlled much of Syria and Iraq. The shocking rise of ISIL led Obama to launch fresh military actions in the region beginning in June of 2014. Though ISIL has now been driven out of Iraq and appears to be very much diminished, a small number of American troops are still stationed in Iraq.