But the vast majority of the territory overrun by the Islamic State was historically populated by Sunni Arabs, adherents of the branch of Islam that the group claims to champion and whose interests the militants profess to represent. The vast majority of the 4.2 million Iraqis who have been displaced from their homes by the Islamic State’s war are Sunnis. And as the offensives get underway to capture Mosul, Iraq’s biggest Sunni city, and Raqqa, the group’s self-proclaimed capital in Syria, more Sunni towns and villages are being demolished, and more Sunni livelihoods are being destroyed.

Most Sunnis played no part in the militants’ rise. All are paying a heavy price for the sake of those who did, accelerating and deepening a reversal in the fortunes of the majority sect of Islam that had ruled the region for most of the past 1,400 years.

“ISIS was a tsunami that swept away the Sunnis,” said Sheik Ghazi Mohammed Hamoud, a Sunni tribal leader in the northwestern Iraqi town of Rabia, which was briefly overrun by the Islamic State in 2014 and is now under Kurdish control. “We lost everything. Our homes, our businesses, our lives.”

Across the border in Syria, where the war against the Islamic State is entangled with the complicated conflict between rebels and the government of President Bashar al-Assad, Sunnis are also bearing the brunt of the violence and dislocation. Sunni towns and neighborhoods are being leveled by Syrian and Russian airstrikes. The effort to crush the mostly Sunni rebellion relies heavily on Shiite fighters from Iran, Lebanon and Iraq. Sunnis comprise the vast majority of the 5 million refugees scattered around the region and in Europe, according to the United Nations and the governments of the countries that are hosting them.