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Who is to blame for the rise of Islamic State in Iraq and Syria (ISIS)? The group’s stunning military advances in Iraq and Syria have, together, built the most important safe haven for Islamic extremists since Taliban-held Afghanistan, and possibly ever. So it is important to understand where ISIS came from – and how it got so strong.

The truth, as usual, isn’t simple. No one person or group can be blamed for ISIS’s rise. The Iraqi and Syrian governments played a major role, but so did the United States, Iran, and Gulf monarchies like Saudi Arabia. This doesn’t just shed light on ISIS’s past and on the tangled web of responsibility for its rise. It also illuminates much larger problems: the unpredictability of proxy wars, the danger of unintended consequences, the ways in which conflict can favor extremists, and the scale of how difficult it will be to eliminate all of the factors that have led to ISIS.

This is the most obvious culprit. Iraqi Prime Minister Nouri al-Maliki, a lame duck […]