President Obama said the U.S. will work with a "broad coalition" of foreign partners to combat the Islamic State in his public address on Wednesday, Sept. 10, 2014. (The Associated Press)

President Obama’s strategy to beat back Islamic State militants spread across Iraq and Syria will depend on far more than U.S. bombs and missiles hitting their intended targets.

In Iraq, dissolved elements of the army will have to regroup and fight with conviction. Political leaders will have to reach compromises on the allocation of power and money in ways that have eluded them for years. Disenfranchised Sunni tribesmen will have to muster the will to join the government’s battle. European and Arab allies will have to hang together, Washington will have to tolerate the resurgence of Iranian-backed Shiite militias it once fought, and U.S. commanders will have to orchestrate an air war without ground-level guidance from American combat forces.

“Harder than anything we’ve tried to do thus far in Iraq or Afghanistan” is how one U.S. general involved in war planning described the challenges ahead on one side of the border that splits the so-called Islamic State.

But defeating the group in neighboring Syria will be even more difficult, according to U.S. military and diplomatic officials. The strategy imagines weakening the Islamic State without indirectly strengthening the ruthless government led by Bashar al-Assad or a rival network of al-Qaeda affiliated rebels — while simultaneously trying to build up a moderate Syrian opposition.

All that “makes Iraq seem easy,” the general said, speaking on the condition of anonymity to share views on policy. “This is the most complex problem we’ve faced since 9/11. We don’t have a precedent for this.”

The Syria side of the campaign remains a work in progress at the Pentagon, CIA and White House. The development of an operational plan is further complicated by a lack of intelligence — U.S. drones have not been flying over Islamic State-controlled parts of the country for long — and the absence of allied local forces that can leverage U.S. airstrikes into territorial gains.

The consequence will be a military campaign unlike the opening days of the 2003 invasion of Iraq, when tens of thousands of U.S. troops charged into the country and toppled Saddam Hussein’s government in three weeks. Nor will it resemble the troop surges in Baghdad and southern Afghanistan, when American forces sought to counter militants by protecting the civilian population. Closer analogues, Obama said Wednesday night, are the counterterrorism campaigns the U.S. waged in Yemen and Somalia, in which the United States has relied on drone strikes and the occasional Special Operations raid to kill or capture high-level targets, but placed no American boots on the ground for extended periods. Day-to-day fighting has been left to Yemeni and Somali soldiers.

Those missions have met with success — a U.S. airstrike killed the leader of Somalia’s al-Shabab jihadist movement last week — but both campaigns have dragged on for years and involve far smaller and less-well-financed adversaries than the Islamic State. Although Obama promised a “steady, relentless effort” in a nationally televised address Wednesday night, he also said that “it will take time to eradicate a cancer like ISIL,” using a common acronym for the Islamic State.

Such a mission was not the U.S. military’s preferred option. Responding to a White House request for options to confront the Islamic State, Gen. Lloyd Austin, the top commander of U.S. forces in the Middle East, said that his best military advice was to send a modest contingent of American troops, principally Special Operations forces, to advise and assist Iraqi army units in fighting the militants, according to two U.S. military officials. The recommendation, conveyed to the White House by Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, was cast aside in favor of options that did not involve U.S. ground forces in a front-line role, a step adamantly opposed by the White House. Instead, Obama had decided to send an additional 475 U.S. troops to assist Iraqi and ethnic Kurdish forces with training, intelligence and equipment.

Recommitting ground combat forces to Iraq would have been highly controversial, and most likely would have been opposed by a substantial majority of Americans. But Austin’s predecessor, retired Marine Gen. James Mattis, said the decision not to send ground troops poses serious risks to the mission.

“The American people will once again see us in a war that doesn’t seem to be making progress,” Mattis said. “You’re giving the enemy the initiative for a longer period.”

Supporters of the president’s approach say that the use of U.S. ground troops could easily send the wrong message to Iraqi soldiers, encouraging them to hang back and allow the Americans to fight, and it might discourage Iraq’s new government from moving quickly in efforts win over Sunnis estranged by the previous prime minister, Nouri al-Maliki. “We cannot do for Iraqis what they must do for themselves, nor can we take the place of Arab partners in securing their region,” Obama said.

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U.S. military and diplomatic officials, even those who favored a small number of ground troops, see a path, albeit rocky, to wresting terrain from the militants in Iraq. If the new government of Prime Minister Haider al-Abadi acts inclusively — a key early test will be whom he selects for the still-unfilled posts of defense minister and interior minister — and his military leaders place competent generals in charge of the reconstituted units dispatched to fight the militants, the Islamic State’s territorial gains could be eroded.

It will almost certainly be a grueling fight. Once U.S. airstrikes intensify and the Iraqi army gets back into the fight, most likely augmented by Shiite militias, members of the Islamic State may go covert, blending in with the local population and conducting insurgent-style attacks on Iraqi troops.

U.S. and Iraqi leaders hope to peel away Sunni tribesmen who have acquiesced to the militants — some of them had viewed the Maliki government as worse for them than the Islamic State — a breakthrough that could help the government’s drive to reclaim territory, but many tribesmen remain wary of promises in exchange for cooperation from Washington and Baghdad. U.S. commanders promised them jobs in the Iraqi security forces if they fought against al-Qaeda’s Iraq affiliate in 2007 and 2008. They fought, but Maliki eventually reneged on those commitments.

“This isn’t going to be as simple as rolling up the highway to Mosul,”said a senior U.S. military official involved Middle East strategy, referring to a large northern city that the militants quickly captured as they surged into the country.

Even so, the prospect of the Iraqis retaking major cities now held by the Islamic State is far less murky than the potential outcome in Syria, which is embroiled in a four-way civil war: the Assad government vs. the Islamic States vs. the al-Qaeda-affiliated al-Nusra Front vs. the moderate but fledgling Free Syrian Army.

“Figuring out where we can strike ISIL so that it weakens them and empowers a more moderate Sunni group instead of the government — you have to think that one through,” said Michele Flournoy, a former U.S. undersecretary of defense. “I’m not sure we know yet how to pull that off.”

Although Obama has previously called for Syria’s Assad to cede power, he did not repeat that call in his address on Wednesday night, perhaps because Iraq’s campaign against the Islamic State is likely to rely on assistance from neighboring Iran, which has long been a supporter of Assad.

He said his request to Congress for additional U.S. resources to train and equip Assad’s moderate opponents was aimed at “pursuing the political solution necessary to solve Syria’s crisis.”