The situation in western Iraq is indeed dismaying. Let's ransack the strategic canon for a few ideas that may help statesmen and commanders comprehend what has happened and what it all portends. First, scholar Timothy Lomperis reminds us that, at bottom, internal struggles such as the one raging in Iraq and Syria are contests for political legitimacy. Whichever contender best provides ordinary people the basics of life, makes a critical mass of the populace a stakeholder in its rule, and ultimately makes them believers in its right to rule is apt to prevail.

Which, second, makes the Iraqi forces' collapse all the more disquieting. There is no way a U.S.-equipped and -trained military serving a legitimate regime — a legitimate cause — should throw down arms and capitulate to a vastly outnumbered enemy, no matter how motivated or well led