A motorist passes by a flag of the Islamic State group in central Rawah, 175 miles (281 kilometers) northwest of Baghdad, Iraq, on July 22, 2014.

Islamic State militants pass a checkpoint bearing the group’s trademark black flag in the village of Maryam Begg in Kirkuk, 180 miles north of Baghdad, Iraq, Sept. 29, 2014. (AP Photo/Hadi Mizban) ...

Abu Bakr al-Baghdadi declared the establishment of the Islamic State caliphate in Iraq and Syria. Following this, ISIS launched a major offensive in northern Iraq and Syria.

Islamic State militants were already resurgent last year in parts of Syria and Iraq. Then in December, the Assad regime collapsed, furnishing them with fresh supplies of weapons from stocks ...