The recent offensive launched by the Sunni insurgents of the Islamic State of Iraq and Syria (ISIS) is the most significant threat to Iraq’s security since the American withdrawal in 2011. The al-Qaeda offshoot has united thousands of foreign fighters under its black flag and a desire to redraw Middle East borders in order to create an Islamic state—or Caliphate—governed by an extremist interpretation of Islamic law.

Militants seized a number of cities and small towns in a lightning assault south toward Baghdad over the past week, displacing hundreds of thousands of people and igniting a global debate about how to respond. They boasted of executing 1,700 soldiers, but the authenticity of that claim is in question. As concerns ramp up that one of the world’s top oil producers is again teetering on the brink of a sectarian civil war, here are the main things you need to know about the regional crisis:

1. ISIS leader Abu Bakr al-Baghdadi is the new public enemy No. 1

Little is known about the man shepherding thousands of radicals between Syria and Iraq. Also called Abu Dua, he was aligned with al-Qaeda leader Ayman al-Zawahiri before the two broke ties over ISIS’ brutal tactics. Baghdadi is arguably the most successful Islamist terrorist since Osama bin Laden—not even bin Laden managed to control a large stretch of territory in Arab lands—and the State Department is offering a $10 million reward for his capture.

2. Nouri al-Maliki, Iraq’s Prime Minister, has made sectarian tensions worse

Two main reasons why ISIS tore through Iraq’s Sunni heartland so quickly—soldiers ran away when ISIS converged on Mosul, Iraq’s second-largest city—can be traced to Maliki. Iraq’s security forces are weak, despite billions of American dollars spent on training, and the absence of national unity has deeply polarized the political landscape. Maliki and his Shi’ite-dominated government are resented by many Sunnis and Kurds for what they see as sectarian rhetoric and policies that have denied them representation and support.

“Maliki has intimidated and driven key Sunni figures out of his government, ignored agreements to create a national unity government, alienated the Kurds and tried to repress legitimate Sunni opposition in ways that have contributed to steadily rising violence and civilian deaths,” write Anthony H. Cordesman and Sam Khazai of the Center for Strategic and International Studies. Maliki’s undermining of the judicial system, police and army for his own advantage, they say, have kept the country vulnerable to power grabs. “With nowhere else to go,” writes Dexter Filkins of the New Yorker, “Iraq’s Sunnis are turning, once again, to the extremists to protect them.”

3. The Kurds may inadvertently gain from the ISIS offensive

Iraq’s Kurdish minority enjoys a semi-autonomous enclave in the northeast that has largely been spared the attacks that plague Iraq. But the new strife could heighten friction between the Kurds, Sunnis and Shi’ites since the Peshmerga—the Kurdish security forces—filled the power void in Kirkuk after Iraqi soldiers retreated. The Kurds have long sought control of the oil city, which they call its historical capital.

That development could contribute to Iraq splitting along sectarian lines. “This would be a further prelude for the division of Iraq,” Brig. Halgord Hikmat, spokesman for the Kurdistan Regional Government’s Peshmerga Ministry, told the Wall Street Journal. “A united Iraq is not the solution at this moment.” Partition would breed a host of other issues, but with Shi’ite clerics encouraging thousands of followers to pick up arms and counter the Sunni insurgents, the Kurds—left off the map after World War I and seeking their own state—could win out.

4. Any crackdown on ISIS could help Syrian President Bashar Assad

The region has been irreversibly impacted by Syria’s civil war. Turkey, Jordan and Lebanon are grappling with humanitarian crises as millions of Syrians have sought refuge in those countries. But Iraq has fared the worst: Parts of its border with Syria have been erased by ISIS, which took the cities of Fallujah and Ramadi in January and controls swaths of several provinces, and Baghdad is rocked by regular bombings.

The ultra-extremists have flourished in Syria by seizing territories that were poorly run by opposition factions. Brutal takeovers have been followed by what Aaron Zelin, a fellow at the Washington Institute for Near East Policy, describes as “soft-power outreach.” ISIS holds anti-regime forums in neighborhood squares and fun activities for children to gain early support, and also hands out charity while promoting its mandate. Zelin adds: “ISIS is attempting to lay the groundwork for a future Islamic state by gradually socializing Syrians to the concept.”

A stronger ISIS bodes ill for Assad. Facing two battles, one to keep or reclaim territory and the other to win back hearts and minds, he could benefit from outside help to beat the insurgency. One idea proposed by a senior policy analyst at the RAND Corporation is a deal between Damascus and the West to bring peace to vulnerable areas and allow Assad to focus on regaining land: “Assad could help NATO and other willing partners focus time and resources on ISIS, which poses the greatest threat to the Middle East, the United States, and Europe.”

5. Iran wants ISIS stopped

The Islamic Republic has played a major role in propping up the Assad regime. But that assistance has not proven a deal-breaker as Tehran and Western powers work to resolve the nuclear standoff. Political leaders on both sides of those negotiations see ISIS as a growing threat and speculation is rampant they may work alongside each other to quell it.

“We will fight against terrorism, factionalism and violence,” Iranian President Hassan Rouhani said on June 12. Days after a report emerged that units of Iran’s elite Quds Force were dispatched to protect allies in Baghdad and the sacred Shi’ite sites of Najaf and Karbala, Rouhani clarified that Iran is ready to help Iraq—if asked—and would consider “cooperation” with any American efforts. (Military decisions rest with its Supreme Leader, Ayatollah Ali Khamenei.)

6. The U.S. is likely to tread softly

The White House has so far resisted committing serious aid to helping Iraq fight the insurgents. It was criticized for not doing enough to ensure security before its withdrawal, which came after Washington and Baghdad failed to agree on conditions for leaving a residual contingent to, among other priorities, keep training security forces and supporting intelligence efforts against Sunni extremists. Obama wanted America’s bravest back home, but it was an overly stubborn Maliki who ultimately doomed the sensitive negotiations.

What’s happening now is direct fallout, as Iraq couldn’t stand on its own. Obama understands this, saying last week that he wouldn’t “rule out anything because we do have a stake in making sure that these jihadists are not getting a permanent foothold in either Iraq or Syria.” Defense officials are now mulling options that don’t include boots on the ground. But if there is any takeaway from Obama’s address on June 13, during which he asserted “we will do our part” while casting blame on Maliki for authoritarian policies that fueled division among the sects, it’s that what is happening in Iraq is no longer America’s problem. That doesn’t mean he won’t work with an adversary or two to solve it.

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