For around 15 years, many American leaders — including all three presidents in that period — believed that the country was too deeply entangled in trying to reorder the societies of the Middle East. They felt the more pressing challenges included rebuilding America’s industrial base and confronting the rise of China. Yet here America is, once again, fighting a war to reorder a society in the greater Middle East. And like in Iraq, Afghanistan and Libya, this war seems unlikely to turn out quite as its proponents may hope. Why does this keep happening? To understand the present, look at...