While the world’s attention has been mainly focused on the war in Gaza, the deteriorating situation in eastern Ukraine, and the Ebola outbreak in West Africa, the Islamic State’s campaign of terror in both Syria and Iraq has seen some of its bloodiest days so far.Things seemed to have reached a stalemate in Iraq, with ISIS’s rapid advance through the country stopped short of Baghdad and the predominantly Shiite areas of southern Iraq. All the same, more than 1,700 Iraqis were killed in July, making it one of the deadliest months since the height of the Iraq war.Then, last week, ISIS captured three towns in northern Iraq from Kurdish forces and now appears to have taken control of the country’s largest dam. It marks the first defeat of the Kurdish Peshmerga forces, and threatened the Kurdish capital, Irbil.Members of the small Yazidi ethnic group in northern Iraq have perhaps fared the worst. Driven from their towns, between 10,000 and 40,000 predominantly Yazidi civilians were stranded on a barren mountain with few supplies. Who are the Yazidis?There are about 600,000 Yazidis worldwide, mostly in Iraq, Iran, Turkey and Syria. Though often considered an offshoot of the Kurds, they consider themselves a distinct ethnic group. They follow a unique religion that blends elements of Sufi Islam and Zoroastrianism. ISIS considers them apostates and has killed at least 500 Yazidis thus far.Why is the U.S. intervening only now?While the U.S. sent 300 military advisers to Iraq last month, the Obama administration has been wary of direct military intervention on behalf of the Iraqi government, making such aid contingent upon the formation of a more inclusive government that gives greater political representation to Sunnis and Kurds, and preferably one without Prime Minister Nouri al-Maliki in charge.But Maliki has shown no willingness to form such a government, and in the meantime the lay of the land in Iraq has worsened. The situation facing the Yazidis has been called a potential genocide, with President Obama himself using the G-word Thursday night. The taking of the Mosul Dam could portend catastrophic consequences. And Kurdistan’s Peshmerga forces, thus far considered the only fighting force in Iraq capable of rolling back ISIS, have now been dealt a string of major defeats. Meanwhile, ISIS fighters are reportedly getting dangerously close to Baghdad.What will a U.S. intervention entail?There doesn’t seem to be much reason to doubt the president when he says that “American combat troops will not be returning to fight in Iraq.” This administration has shown little enthusiasm for intervention in either Iraq or Syria and will likely try to keep this mission as limited as possible.Of course, all interventions are subject to mission creep, and a limited campaign of airstrikes to “prevent a potential act of genocide,” as the president put it, could easily turn into a longer air campaign on behalf of the Iraqi government against ISIS, a somewhat awkward proposition given Iran’s role as Baghdad’s primary patron.How does this end?While essentially every government in the Middle East is united in its opposition to ISIS, nobody seems able to stop it. (In addition to its gains in Iraq, the group recently made its first major foray into Lebanon.) So far, it has worked to the group’s advantage that many of the governments it is fighting — Syria, Iraq, the United States, Iran, Kurdistan — are also at odds with each other. Whenever the group faces a setback on one front, it seems to melt back into the wilderness and launch a new campaign somewhere else.Ironically, ISIS’s campaign against the Kurds may end up helping unify the Iraqi state. Until last week, it looked like the destabilization caused by ISIS’s rampage through the country would aid the cause of Kurdistan, which has been pushing for full independence from Iraq for years and had been feuding with Maliki’s government over oil revenues. Now, Maliki is ordering his air force to help the Kurds. Iraq’s various factions, as well as Baghdad’s odd-couple patrons, Iran and the United States, may be forced to work together to confront the most serious threat the country has faced since the worst days of the Iraq war. Joshua Keating is a staff writer at Slate focusing on international news, social science and related topics.