To many, President Barack Obama’s authorization of airstrikes in Iraq -- and their commencement a few hours ago -- appears to be a major shift in U.S. posture. Certainly, this is the hope of millions of Kurds, tens of thousands of Yezidis, and countless other Iraqis desperate to stave off further gains by the radical fighters of the Islamic State in the Levant. Undoubtedly, it was a tough decision for the president, who has long been reluctant to use force in the Middle East and has prided himself on having "ended" the war in Iraq.

But is the shift as consequential as it seems? Obama's rhetoric on Thursday suggests we should be cautious in over-interpreting the turn of events, and very concerned about the sustainability of American engagement.

U.S. hesitation on Iraq creates opportunities for Iran

In his efforts to save Iraq, President Obama is right to demand more power-sharing and other political reforms from Iraqi leaders before the United States offers more military assistance. But Obama should not think he can hold off offering such assistance until he secures those reforms—not if he wants to prevent the bloody breakup of the country and a wider regional war. As sensible as a conditional approach seems, the president simply doesn’t have that option open to him.

In a Harvard Kennedy School IDEASpHERE session titled "Challenges to US Global Leadership," Graham Allison, Nicholas Burns, David Gergen, David Ignatius, and Meghan O’Sullivan discussed challenges as well as opportunities facing the United States. Burns moderated the session.

Challenges include the rise of China and the future of the U.S.-China relationship, the crises taking place around the world, and the reputation of the U.S. worldwide. An unexpected opportunity is the increase in available energy sources in the United States.

Many Americans are surprised to see Fallujah back on thefront pagesof newspapers. How did things get so bad that the Iraqi government was compelled to call for American support in its battle against an al-Qaeda affiliate, the Islamic State of Iraq and Syria?

April marks the tenth anniversary of the overthrow of Saddam Hussein by the United States and its partners. At this juncture, it is reasonable for Americans—and Iraqis and others—to ask whether the past decade of U.S. involvement in Iraq was worth it. Did the large human and financial costs produce an outcome that justifies the sacrifice?

"As America looks back on this 10th anniversary of the Sept. 11 attacks, the war in Iraq looms large — and usually not in a good way," writes Meghan O'Sullivan. "At best, it’s regarded as a distraction, a needless conflict that took America’s focus away from Afghanistan and al-Qaeda. At worst, the Iraq war is decried as a fiasco, the United States’ 'greatest strategic disaster,' as retired Gen. William Odom, the former National Security Agency director, once put it."

Meghan L. O'Sullivan is a lecturer in public policy at Harvard Kennedy School's Belfer Center for Science and International Affairs. From July 2004 to September 2007, she was special assistant to President George W. Bush and served as deputy national security advisor for Iraq and Afghanistan during part of that tenure. She spent more than two years in Iraq, most recently in fall 2008 at the request of Ambassador Ryan Crocker and General Raymond Odierno, to help conclude the security agreement and strategic framework agreement between the United States and Iraq.

Adecade after the removal of Saddam Hussein, we still appear reluctant to embrace one of the central lessons of Iraq: that regime change necessitates nation building. This lesson—and the many subsidiary lessons that flow from it—is of real relevance to what is happening in the Arab world today.