President Obama was right to order airstrikes against the ISIS home base in northern Syria Monday night. There was no alternative but to target ISIS headquarters in Raqqa and other locations where the terrorist group has built up a considerable infrastructure.

The US strategy to contain ISIS and to prevent it from dismembering Iraq cannot succeed without weakening and ultimately destroying ISIS where it was created — in Syria. Obama understands that the extraordinary swift and sudden ISIS advance from Syria into Iraq in early summer effectively created one Iraq-Syria battle space. To contain and ultimately destroy ISIS — which is the administration’s stated goal — it will have to operate militarily in both countries.

Monday night’s US-led airstrikes were significant for another reason — the direct involvement by fighter jets from the leading Sunni Arab countries, including Saudi Arabia, Jordan, Bahrain, and the United Arab Emirates. Obama also understands that the fight against ISIS is, at its core, a struggle for the future of the Sunni world. It was critically important that Sunni governments give clear and active public support to the US effort. This is, in reality, their fight and it will be important that they sustain their military involvement as this campaign goes forward.

Ultimate success against ISIS, however, will depend on the United States helping to pull together a ground component to match the air campaign. ISIS is too strong, too entrenched, and too wealthy to be defeated by air power alone. This means the United States will have to equip and train the Kurdish peshmerga forces to protect Iraqi Kurdistan against ISIS assault. The United States will also have to help reconstitute, retrain, and rearm a dissolute and ineffective Iraqi army that was routed in Mosul this summer by a much smaller ISIS force.

An effective ground component must also be built in Syria itself. That is why the entire strategy depends on doing what Obama has resisted for nearly four years — sustained, substantial arming and training of the moderate Syrian rebel forces, such as the Free Syrian Army. Despite the administration’s pledge to do just this, it remains to be seen if the United States will, in fact, fully commit to this difficult but essential part of the overall strategy.

In less than two months, the United States has gone back into the Iraqi cauldron. This must have been the most wrenching of decisions for Obama, whose national career was built on opposition to George W. Bush’s war there. He was forced by ISIS’s powerful assault into Iraq this summer to commit US Special Forces to connect with the Iraqi and Kurdish forces and to protect our embassies and consulates in Iraq from ISIS attack. As the US campaign continues, Obama may have to introduce more such enabling forces to help direct the air attacks from the ground.

But Obama is right to resist re-introducing substantial ground combat forces back into Iraq. There is little or no public and congressional support for another American occupation. It would risk many of the same cruel frustrations of our difficult, indeed torturous, eight-year venture in Iraq from 2003 until 2011. And it would undermine the essential point Obama has been making to the Iraqi government and its Sunni Arab neighbors — this has to be your fight.

Monday night’s airstrikes are not a quick fix for what will surely be an enormously complex and risky US campaign. Americans should expect this to be a long, dangerous, and often frustrating mission. But we would be derelict in strategic and even moral terms if we left unopposed a vicious and predatory terrorist group that could ignite an even more bloody regional war engulfing not only Iraq and Syria, but also neighboring Jordan, Lebanon, and even Turkey.

Obama has launched a new and necessary phase in the battle against ISIS. It is a fight we did not seek but must now pursue.