Stephen J. Hadley, a principal at RiceHadleyGates LLC, was national security adviser in the George W. Bush administration.

Ten years on , public views of the war in Iraq are still highly politicized and partisan. As passions cool, what should Americans conclude about the war?

1. The war went too long and cost too much — in the lives and treasure of Americans, our coalition partners and Iraqis. The quick toppling of Saddam Hussein in 2003 was followed by a prolonged insurgency and sectarian violence that threatened to tear Iraq apart. It was the responsibility of the U.S.-led coalition to prevent this, and we didn’t.

We also did not anticipate that al-Qaeda would move into the security vacuum created by Hussein’s fall and seek to defeat the United States in Iraq. Ultimately, history is likely to show that the Pakistani-based “core” of al-Qaeda responsible for 9/11 was defeated in Iraq. But it was a long, hard struggle.

2. After more than three years of escalating violence and increasing sectarianism, the United States and its allies turned around a war that we were not winning. President George W. Bush made a bold decision in 2007 to change strategy and add 30,000 U.S. troops. Working with coalition and Iraqi counterparts, U.S. troops, intelligence officers and diplomats implemented the “surge” with imagination and courage — and largely ended the violence. Agreements Bush signed in December 2008 established the terms for an enduring bilateral partnership and the schedule for withdrawal of U.S. forces. President Obama, who as a senator had opposed the surge strategy that made it possible, implemented the withdrawal plan, and U.S. military forces were out of Iraq by the end of 2011.

3. Ultimately, the United States achieved its national security objectives. Today’s Iraqi government does not pursue weapons of mass destruction, support terrorists, invade its neighbors or brutally oppress its people. Hussein had done all these things, despite some 17 U.N. Security Council resolutions calling on him to stop. The United States went to war because of his failure to stop after 12 years of international diplomatic effort, economic sanctions, “no-fly” zones, various inspection regimes and limited military strikes ordered by President Bill Clinton.

After Hussein was deposed, we did not find the stockpiles of WMDs that all the world’s major intelligence services, the Clinton and Bush administrations and most members of Congress thought that he had. It was less an intelligence failure than a failure of imagination. Before the war, no one conceived what seems to have been the case: that Hussein had destroyed his WMD stocks but wanted to hide this from his enemy Iran. The U.S. team charged with searching for WMDs concluded that Hussein had the intention and the means to return to WMD production had he not been brought down. (With Iran pursuing nuclear weapons, it is a good bet that he would have.)

4. The U.S.-led postwar reconstruction and stabilization effort was fraught with problems and failed to accomplish what we hoped for or what Iraqis expected. A lot of mistakes were made. While the United States has invested heavily in its military for decades, it has not made a comparable investment in the civilian capabilities and institutions needed to help postwar societies build reliable security institutions, ignite economic growth and deliver basic services.

Our nation needs these capabilities, not because it is contemplating more such military operations but because these skills are necessary to help prevent failing states (such as Somalia and Yemen) and post-revolutionary states (such as Tunisia, Egypt and Libya) from descending into chaos. Conflict avoidance is vastly cheaper in lives and treasure than either military intervention or a society being torn apart, as Syria is today.

5. Despite all the problems, by 2008-09 Iraq could govern, defend and sustain itself, and it was an ally in the war against terrorism. Sporadic violence continued but was not a strategic threat to the state nor beyond the capability of Iraqi security forces. Iraq had a democratic government in which Shiites, Sunnis and Kurds worked together for a common future. The United States and its coalition allies did not go to war to impose a democracy on the Iraqi people. But having toppled Hussein, President Bush decided that we owed Iraqis the chance to build a democracy with our help. And they took it. While the Iraqi leadership appeared to be a fractious group lurching from crisis to crisis, the new government held together and began to work. This was no small feat in a region where all too frequently Sunnis oppress Shiites, Shiites oppress Sunnis and both beat up on the Kurds.

6. The Arab Spring increasingly leaves these achievements at risk. Revolutions in Tunisia, Egypt and Libya have caused regional instability. Iran is pressuring Iraq from the east, Turkey from the north and Syria from the west. The failure to keep a modest U.S. military presence in Iraq has reduced not only Washington’s ability to counterbalance this pressure but also U.S. influence in Iraq. Syria is particularly worrisome: more than 70,000 dead, 1 million refugees and more than 2 million internally displaced. With no end to the fighting in sight, sectarian violence is spilling over into neighboring Lebanon, Jordan, Turkey and Iraq.

Destabilizing these states would threaten not only broader U.S. interests in the region but also the enormous investment the United States has made in Iraq. This is one more reason many of us believe our nation should be more active in supporting the opposition — and ending the violence in Syria.