The Islamic State breaks with al-Qaeda, takes Raqqa from other rebel factions in 2013–14, seizes Mosul in June 2014 and declares a caliphate spanning the Iraqi–Syrian border — at its peak ruling some eight million people and fighting regime, rebels and Kurds alike.
Why it mattersISIS reordered the war's international meaning: counter-ISIS became the world's Syria policy, saving the Assad government strategically and creating the US–Kurdish partnership that shaped the northeast for the next decade.