Shiite volunteers prepare to fight against Islamic State. Photographer: Haidar Mohammed Ali/AFP/Getty Images
Shiite volunteers prepare to fight against Islamic State. Photographer: Haidar Mohammed Ali/AFP/Getty Images

President Barack Obama's decision to launch airstrikes against Islamic State in Iraq was correct -- though not for the reasons he gave. This jihadi movement is a major threat to the U.S. and its interests in the Middle East. That's what justifies use of force against it.

Announcing the action, Obama stressed his determination to keep the U.S. out of a new war, and said the airstrikes were an exception to his policy of non-involvement. He said the threat of genocide against the Yazidi people and the risk to U.S. personnel stationed in the Kurdish capital Erbil had forced his hand.

Those were reasons to act but not the main reason. Caution in the use of force is always wise, and Obama is certainly right that Americans don't want to fight another war in the Middle East -- but let there be no illusions about the larger danger posed by Islamic State.

This flourishing organization, formerly Islamic State in Iraq and the Levant, is both a jihadi-run failed state in the making and an increasingly formidable military force. It's at least as worrying to U.S. and European intelligence chiefs as al-Qaeda and its branches in Yemen, which the U.S. rightly attacks when it can. The danger of mission creep must always be kept in mind, but the U.S. military has many options that permit timely and effective action short of war.

Unchecked, Islamic State will present the U.S. with an ever-expanding range of problems demanding intervention -- from Baghdad, to Erbil, to Jordan and Syria and eventually at home and in Europe. No doubt in each case the intervention could be justified as an exception. It would be better for Obama to acknowledge, and explain, the encompassing problem.

Islamic State is not al-Qaeda. The group's leader, Abu Bakr Al-Baghdadi, fell out with al-Qaeda over a turf war in Syria and an ideological rift over whether to focus first on attacking the Western infidels or on building a caliphate. That's an argument over timing and methods. (On the latter, Islamic State isn't so moderate as al-Qaeda.) The intent, though, is clear enough: "I'll see you guys in New York," al-Baghdadi told his captors after leaving a U.S. jail in Iraq in 2009.

So long as Islamic State controls the Sunni areas of Iraq, Obama's goal of securing a unified Iraq is unachievable. Meanwhile, the danger the organization poses beyond the region will grow. Europol estimated that as many as 2,000 Europeans were fighting in Syria at the end of last year, most of them with Islamic State. The grim prospect is a caliphate that becomes a recruitment and training center for global jihadis.

The cost to the U.S. of helping Iraqis to counter Islamic State remains low for now. This can best be done by arming the Kurds so they can defend themselves (and the Yazidis, Christians, Turkmen and other minorities vulnerable to genocide in northern Iraq), and with airstrikes against targets of opportunity, when the jihadis' trucks and stolen Humvees are strung out across Iraq's desert roads.

Islamic State is the greatest challenge to U.S. interests in Iraq. Next time -- and there will be a next time -- that's what Obama should say.

To contact the senior editor responsible for Bloomberg View's editorials: David Shipley at davidshipley@bloomberg.net.