1. What you need to know about

2.  The Islamic State of Iraq and the Levant (ISIS) used to have a different name: al Qaeda in Iraq.  US troops and allied Sunni militias defeated al Qaeda in Iraq during the post-2006 "surge" — but it didn't destroy them.  In 2011, the group rebooted. ISIS successfully freed a number of prisoners held by the Iraqi government and, slowly but surely, began rebuilding their strength.  ISIS and al-Qaeda officially separated in February 2014  Syria pushed that relationship to the breaking point. ISIS claimed that it. ISIS also defied repeated orders to kill fewer civilians in Syria, and the tensions led to al-Qaeda disavowing any connection with ISIS in a February newsletter.  Today, ISIS and al-Qaeda compete for influence over Islamist extremist groups around the world. Some experts believe ISIS may overtake al-Qaeda as the most influential group in this area globally.

3.  Their goal since being founded in 2004 has been remarkably consistent: found a Sunni Islamic state.  They want to establish a caliphate in Iraq." Even after ISIS split with al-Qaeda in February 2014 (in large part because ISIS was too brutal for al-Qaeda) ISIS' goal remained the same.  Now, they have no chance of accomplishing any of these things in the foreseeable future. ISIS isn't even strong enough to topple the Iraqi or Syrian governments at present. But these maps do tell us something important about ISIS: they're incredibly ambitious, they think ahead, and they're quite serious about their expansionist Islamist ideology.

4.  Perhaps the single most important factor in ISIS' recent resurgence is the conflict between Iraqi Shias and Iraqi Sunnis. ISIS fighters themselves are Sunnis, and the tension between the two groups is a powerful recruiting tool for ISIS.  The difference between the two largest Muslim groups originated with a controversy over who got to take power after the Prophet Muhammed's death. But Iraq's problems aren't about reiterating 7th-century disputes; they're about modern political power and grievances.  A majority of Iraqis are Shias but Suddam Hussain was Sunni and so Sunnis had control until Saddam was overthrown after US invasion, giving power back to the Shias.  Today, the two groups don't trust each other, and so far have competed in a zero-sum game for control over Iraqi political institutions. (For example, Shia used control over the police force to arbitrarily detain Sunni protestors demanding more representation in government last year.)  So long as Shias control the government, and Sunnis don't feel like they're fairly represented, ISIS has an audience for its radical Sunni message. That's why ISIS is gaining in the heavily Sunni northwest.

5.  ISIS would be able to recruit Sunni fighters off of the Sunni-Shia tension even if Iraqi Prime Minister Nuri al-Maliki weren't in office, but his policies towards the Sunni minority have helped ISIS considerably.  Iraqi Prime Minister Nuri al-Maliki, a Shia Muslim, has built a Shia state and refused to take steps to accommodate Sunnis.  Police have killed peaceful Sunni protestors and used anti-terrorism laws to arrest Sunni civilians. Maliki has made political alliances with violent Shia militias, infuriating Sunnis. ISIS exploited that brutality to recruit new fighters.  The US and Iraqi governments released a huge number of al-Qaeda prisoners from jail, which called "an unprecedented infusion of skilled, networked terrorist manpower - an infusion at a scale the world has never seen." US forces were running sophisticated raids "every single night of the year," and their withdrawal gave ISIS a bit more breathing room.

6.  The crisis in Syria is one of the most important reasons why ISIS grew capable of mounting such an effective attack on the Iraqi government. To see why, take a look at this map from March, paying special attention to the blue ISIS-controlled areas in eastern Syria:  The chaos in Syria allowed ISIS to hold this territory pretty securely. This is a big deal in terms of weaponry and money. The war gave them a lot of access to heavy weaponry and ISIS also has a funding stream available to them because of local businesses and the oil and gas sector.  It's also hugely important as a safe zone. When fighting Syrian troops, ISIS can safely retreat to Iraq; when fighting Iraqis it can go to Syria. Statistical evidence says these safe "rear areas" help insurgents win: one of the best predictors of insurgent success that we have to date is the presence of a rear area.

7.  ISIS doesn't depend on foreign aid to survive. In Syria, they are collecting the equivalent of taxes, selling electricity, and exporting oil to fund its militant activities.  ISIS is selling electricity to the Syrian government that it's currently fighting.  There are two important takeaways here: First, these clever revenue bases have made ISIS much more effective on the battlefield than other militant groups.  This money goes a long way: it pays better salaries than moderate Syrian rebels or the Syrian and Iraqi professional militaries, both of which have suffered mass desertions. ISIS also appears to enjoy better internal cohesion than any of its state or non-state enemies, at least for the moment.  Second, it makes the idea that ISIS' near-term goal is to hold Iraqi oil and power facilities more credible..  ISIS sees oil as an important part of its future development.

8.  This conflict often gets portrayed as a fight between the Iraqi government and ISIS. That's overly simplistic on two levels: the Iraqi government has assistance from Iran and Shia militias, while ISIS isn't the only group battling the Iraqi government.  The most important rebel group beyond ISIS is Jaysh Rijal al-Tariqa al-Naqshbandia (JRTN). They're Sunni nationalists, many of whom are former members of Saddam Hussein's Baath party.  Of the two, ISIS is stronger.

9.  ISIS' major breakthrough was a victory in Mosul, a northern Iraqi city and the country's second most populous. Since then, they've made rapid advances.  Combine that with ISIS territory in Syria, and they control a territory that some experts say amounts to roughly the area of Belgium

10.  ISIS cannot challenge the Iraqi government for control over the country. On a basic level, it's simple math. ISIS' fighting strength suggests is bit more than 7,000 combat troops, and it can occasionally grab reinforcements from other extremist militias. The Iraqi army has 250,000 troops, plus armed police. The Iraqi military also has tanks, airplanes, and helicopters. ISIS can't make a serious play for the control of Baghdad, let alone the south of Iraq, without a serious risk of getting crushed.  But the Iraqi army is also a total mess, which explains why ISIS has had the success it's had despite being dramatically outnumbered.  In Mosul, 30,000 Iraqi troops ran from 800 ISIS fighters. Those are 40:1 odds! Yet Iraqi troops ran because they simply didn't want to fight and die for this government. There had been hundreds of desertions per month for months prior to the events of June 10th. The escalation with ISIS is, of course, making it worse.  The Iraqi army is mixed Sunni-Shia, and some Sunni Muslims don't really want to fight other Sunnis in the name of a government that oppresses them.

11.  The Iranian government is Shia, and it has close ties with the Iraqi government. Much like in Syria, Iran doesn't want Sunni Islamist rebels to topple a friendly Shia government.  In June, Iran sent about 500 Revolutionary Guards to help Iraq fight ISIS. These aren't just any old Iranian troops. They're Quds Force, the Guards' elite special operations group. The Quds Force is one of the most effective military forces in the Middle  Iran's military, especially Quds Force fighters, outclass ISIS on the battlefield. But Iranian intervention could also help ISIS in its quest to build support among Iraq's Sunnis. The perception that the Iraqi government is far too close to Iran is already a problem among Sunnis.  So Iranian participation in actual combat risks legitimizing ISIS' propaganda line: this isn't a conflict between the central Iraqi government and Islamist rebels, but rather a war between Sunnis and Shias.

12.  The US and Iran have been at odds for decades in the Middle East over issues like the Iranian nuclear program, the second Iraq war, Syria, and Israel. Yet both the United States and Iran want the Iraqi government to beat back ISIS, and the two traditional enemies have met to talk about what they can do together.  Informal talks between US and Iranian leadership in June 2014, but they never came to an open agreement.  Iranian leadership has signaled openness to working with the United States on Iraq issues, but the Obama administration has yet to take Iran up on the offer to cooperate (at least, in the open).  There's a distinct possibility the United States will sanction a wider Iranian military intervention in Iraq — despite American troops spending years fighting Iranian-backed militias after the US invasion in 2003.  If any agreement comes out of US-Iran talks, it'll be both difficult and controversial in both countries. Many American and Iranian strategists see the other as a, if not the, primary enemy in the Middle East.

13.  President Obama announced on August 7, 2014, that he had authorized the US military to launch air strikes against ISIS militants in Iraq if they threatened thousands of civilians trapped on Mount Sinjar in northern Iraq.  The ISIS militants have pushed into once-secure Kurdish territory and have surrounded thousands of civilians, on a mountain where they lack food and water.  The ISIS crisis may be the most devilish foreign policy problem of Obama's presidency, pitting two pillars of his administration's foreign policy against each other: his strategy of using targeted killings to counter violent extremism versus his ironclad commitment to ending war in Iraq.  In June, Obama sent up to 575 American troops to Iraq but most are tasked solely with providing security to personnel evacuating the Baghdad embassy.  The Iraqi government has been quietly requesting American military aid in the form of drone strikes against ISIS.  In a press conference on June 13th, Obama ruled out the deployment of US ground troops. He did leave open the possibility of US airstrikes, and has moved cruise missile destroyers into the Persian Gulf.  The United States is not simply going to involve itself in a military action in the absence of a political plan by the Iraqis that gives us some assurance that they're prepared to work together.  At that point, it seemed, Obama had ruled out the most likely scenario for military action in Iraq: a short-term aerial campaign designed to help the Iraqi military halt ISIS' momentum.  That said, subsequent Obama statements have relaxed that criterion a bit. "Going forward, we will be prepared to take targeted and precise military action if and when we determine that the situation on the ground requires it," he said on during a June 19 press conference.  There's also a quickly expanding political debate over whether the Obama administration deserves blame for the chaos. The controversy centers around the fact that Obama did not succeed in extending the Bush-era status of forces agreement with Iraq, which stipulated that all US troops had to withdraw from Iraq by the end of 2011. The administration tried and failed to negotiate provisions that would have allowed the United States to leave a number of troops there.

14.  In terms of an endgame, experts see ISIS failing to establish an effective rebel government and the Kurds coming out as big winners (provided the recent fighting in Kurdistan ends favorably)  "The regions [ISIS controls] are not viable entities," Kirk Sowell, a political risk analyst and expert on Iraqi politics, says. "Anbar[, an insurgent-contested Sunni province,] is totally dependent; over 95 percent of their money comes from Baghdad … Ninevah[, another insurgent-contested province containing Mosul,] is going to suffer a complete economic collapse." So "the Sunnis" who live in these provinces and elsewhere "will suffer more from this than anyone," Sowell concludes.  The exception could be, perhaps, Iraqi minority groups. On August 6, ISIS took Qaraqosh, Iraq's largest Christian town. The town of 50,000 has had limited access to food, power, and water since, and some Christians have been given the "choice" to convert to Islam or be killed, with the end result still being death for violating Islamic laws.  Another minority group, the Yazidis, are also being brutalized by ISIS' advance. The largest concentration by far is in northern Iraq, where ISIS recently made significant inroads — including into a heavily Yazidi town called Sinjar. ISIS captured Sinjar on August 3, sending most of its 200,000 residents on the road for fear of being killed by ISIS fighters who are massacring Yazidis for their faith. In fleeing ISIS, between 10,000-40,000 have taken refuge on Mount Sinjar, an adjacent mountain. They have no regular access to water, and are trapped between thirst and ISIS' guns.

15.  James Foley was an American conflict reporter who went missing in Syria almost two years ago. On Tuesday, August 19, a video of Foley surfaced. The video, apparently produced by ISIS as a warning to the US to stop air strikes against the group in Iraq, ended with Foley's death. Titled "A Message to #America (from the #IslamicState)," the video depicts a British-accented ISIS militant forcing Foley to condemn America before beheading him.  Afterwards, ISIS displays a man they claim is another missing American journalist, Steven Sotloff. They threaten to kill him if the US doesn't stop bombing ISIS. And on September 2, ISIS released On September 2, ISIS released a video showing the execution of Steven Sotloff, proof that they had followed through on the threat.  Foley and Sotloff's murders will not end the American air campaign. Longstanding US policy has been to not give in to ransom demands, in part because it creates an incentive for groups like ISIS to kidnap Americans.  The big question after their killings, then, is whether or not the US will ecalate their involvement or strike again against ISIS in response. It's not clear whether ISIS killed Foley and Sotloff in order to 1) get what it says it wants and end the American air campaign or 2) bait the US into an unwise escalation.  On August 28, President Obama said that his administration had yet to develop a specific strategy for addressing the threat posed by ISIS.  More to come…

16.  Two big things have happened much more recently to make the crisis bad enough that Obama might send air strikes. 1. First, ISIS pushed into previously-secure northern Iraq, which is controlled by the country's ethnic Kurdish minority. Kurdish Iraq was considered so secure that the US evacuated its Baghdad embassy staff to the Kurdish city of Erbil, where they still are, putting the Americans under threat from ISIS. That's a big part of why the US is launching air strikes. 2. Second, ISIS sent at least ten thousand civilians from the ethno- religious minority group Yazidi fleeing from their homes and onto the nearby Mount Sinjar. They are still there and have no regular access to food or water; they can't descend the mountain because ISIS will slaughter them. The American humanitarian airdrops will bring the Yazidi water and perhaps food. US airstrikes could also push ISIS back from Mount Sinjar if the US believes ISIS is threatening the Yazidi there.  But remember that all of this goes back to the Iraq War, and al-Qaeda's rise there, and to the more recent Syrian civil war that gave ISIS a base of operations.