ISIS has continued its advance in northern Iraq, taking over three more cities, another oil well, and the largest hydroelectric dam in Iraq, according to Reuters. But what’s even more upsetting is that the Islamic militants did so by handing Kurdish peshmerga forces their first major defeat, which could mean that ISIS is a more significant threat that we had believed.

ISIS

ISIS defeats Kurdish forces, may have been underestimated

When ISIS first rolled into northern Iraq from Syria, where they have been battling Syrian president Bashar al-Assad’s forces for some time, it was seen as evidence that the Iraqi military was neither well trained nor loyal to the Iraqi government. The speculation was that ISIS was able to claim large swathes of territory because they hadn’t met any serious resistance.

That was supposed to change if ISIS eventually went up against Kurdish forces, but they took the Mosul Dam in less than 24 hours. Kurdish officials say that the militia was overstretched, Al-Arabiya reports, and that Kurdish troops are organizing a counterattack with air support from the Iraqi military. Hopefully they will manage to push ISIS back, but today’s Kurdish defeat along with ISIS’s strike in Lebanon over the weekend show how dangerous the group is.

If there’s any upside to all this, and there can’t be much, this could give factions in Iraq more reason to put their differences aside at least long enough to regain control of the country. President Nouri al-Maliki’s decision to send air support to aid the peshmerga could be a sign of better collaboration.

Blowing up Mosul Dam could kill 500,000

Control of the Mosul Dam potentially gives ISIS an enormous bargaining chip: blowing up the dam would flood Baghdad and other major Iraqi cities, with some estimates putting the death toll from the mass flooding at 500,000. Even if they didn’t opt for such a severe option (and nothing we’ve heard about their tactics so far suggests they would stay their hand), they could simply cut off an important supply of water to the south to ratchet up pressure on the Shia-led Iraqi government that they want to overthrow.