There have been many factors to the rise of ISIS, from a relatively obscure Al Qaeda affiliate that had been forced almost completely underground by a combination of US military power and the Sahwa militias in Al Anbar Province (ISIS was originally Abu Musab al Zarqawi’s Al Qaeda in Iraq), to a cross-border rebel/terrorist group in Iraq and Syria that appeared to spend more time fighting with the other Islamist militias than they ever did fighting the regime, to the new terror of the Middle East and policy wonks everywhere.

Some of these factors, as have been examined with varying levels of knowledge in multiple places, have to do with what they are doing and how they have learned a much higher degree of operational and strategic sophistication than their predecessor organization.

However, there is more to any conflict than just what one side is doing. As the old saw goes, “The enemy gets a vote.” In this case, who ISIS is fighting has had a great deal to do with their success on the ground.

In Iraq, ISIS’ primary adversaries have been the Iraqi Army and the Kurdish Peshmerga. The IA almost immediately dissolved in the face of ISIS’ advance in June. The Peshmerga, while generally considered better fighters than their southern Arab neighbors, are a mountain militia, not an army. They have little in the way of heavy weapons, no armor to speak of, and their go-to strategy (that has kept them from being wiped out more than once) is, when it starts to look really bad, head for the hills.