Nineveh is Iraq’s most diverse province, with a dizzying array of ethnic and religious groups woven into an area about the size of Maryland. For centuries, Arabs, Kurds, Christians, Turkmens, Yezidis and Shabaks lived side by side in these verdant hills, going to the same schools, bartering in the same markets, even intermarrying on occasion.But what took generations to build is starting to unravel in the shadow of the Sunni Arab insurgency, which is tapping into several wells of ethnic resentment.