From the very beginning, the center piece of President Barack Obama's foreign policy agenda was winding down the wars waged by his predecessor in Afghanistan and Iraq. He had promised as much to the American people during his campaign and with the last US troops scheduled to leave Afghanistan by the end of 2016, he will have fulfilled his pledge by the time he leaves office.

But beyond ending Bush's wars, Obama has generally shown and articulated a deep skepticism about the use of US military power in global conflicts in his more than five years in office. His caution - critics call it reluctance - is summed up best in the motto that has rightly or wrongly been ascribed to his foreign policy, particularly his opposition to what he considers hasty US military endeavors: "Don't do stupid stuff."

So why did Obama choose to act in Iraq after all and not in Syria, where the conflict between the opposition and President Bashar al-Assad has raged on far longer, claimed far more lives and in which the "Islamic State" has acted just as brutally and also has established a stronghold in the north of the country?

Legal basis

One reason is of course that it's not in the US interest to strengthen the hostile Assad regime by taking on IS, which fights against the Syrian government. But that still does not suffice to explain Obama's decision to intervene now in Iraq.

An important legal precondition for US military action, especially for the Obama administration and its more multilateralist stance, is that Washington has been officially asked by the Iraqi government to militarily intervene in Iraq.

"So there is no problem with abuse of sovereignty," Michael Stephens, deputy director of the Qatar branch of the British think thank RUSI, told DW. "That makes that problem particularly easier." Without an Iraqi invitation, Washington would have needed a UN resolution to not flout international law.

As for the political reasons for the US intervention, James Jeffrey, former US ambassador in Iraq until 2012 and deputy national security advisor to George W. Bush points to President Obama's Iraq speech in June where he outlined his three-pronged policy: counterterrorism and protection of Americans, providing emergency assistance and counterinsurgency support.

All of those points, however, were conditional upon a new inclusive Iraqi government that the country's battered military would even consider worth fighting for, according to Jeffrey.

After Obama announced his policy, everything seemed to calm down and come to a standstill for a while. On the military front, IS advances appeared to lose steam. And on the political front, Iraqi Prime Minister Nouri al-Maliki did not want to heed Obama's message to step down and decided instead to dig in.

Kurdish trigger

"But then suddenly the trigger happened and to everybody's surprise, it was against the Kurds," Jeffrey told DW.

With IS fighters practically overrunning the comparatively well-trained Kurdish peshmerga defenses and threatening Iraqi Kurdistan's regional capital Irbil, direct US interests were at stake.

"There are US personal living in Iraq and many American civilians working in Irbil in the oil industry and other areas," said Stephens, who has travelled to Iraqi Kurdistan eight times this year.

There is also a large expat population generally in Irbil and IS was basically threatening that population, Stephens added. "You did not really have that dynamic in Syria. So I think there is a qualitative difference there."

The oil industry itself in Iraq's Kurdish region, however, does not feature as a motivation for US action. "Oil is a template that is often used to explain events in the Middle East, but it doesn't work here," Stephens said. Kurdish oil output, he noted, is negligible compared to that in the Basra region, and Washington's interests are anyway of a much more geostrategic nature than oil.

Protection of Yazidis

When the Kurdish front cracked surprisingly quickly, everything suddenly came together for the US. Not only were American interests and lives at risk, but with the Kurdish regional government, Washington had a partner it could work with against IS.

Then in a move that fully turned the tide toward US intervention, IS attacked the Yazidi religious minority in Iraq. Washington warned of genocide and deployed first humanitarian assistance to the Yazidis followed by an air campaign against IS.

"It's always a question how one defines genocide," said Jeffrey. "But a large percentage of the world's remaining Yazidis were rounded up and sent off to the mountains to die. While it's not a big group, it's more genocidal then most things that are called genocide."

"If the Americans hadn't intervened, I think what you would have been seeing would have been almost the destruction of a religious minority, and it's complete removal from the Middle East," Stephens said.

Obama's 'German approach'

Jeffrey and Stephens generally support Obama's Iraq policy, but both have serious questions about how it will play out. Due to the Iraqi army's weakness, Stephens worries not only about potential mission creep that could lead to a much broader US military campaign, which particularly Britain and France are lobbying for, but also that deeper engagement could set a new precedent for similar interventions on humanitarian grounds elsewhere.

Jeffrey, however, is more concerned about whether Obama even now possesses the political will to use sufficient air power to cripple IS. Pointing to the president's skepticism to use military force and his multilateralist leanings, he quipped: "It's almost the German government position. That's the problem with it. We are not the German government. We are the one that the German government and everybody else turns to to lead."