One of the most surprising gains for ISIS was their capture of the second-largest city in Iraq, Mosul. But two years later, the terrorist organization has lost about half their territory in Iraq overall. Forces backed by the U.S. recently launched an operation to take back Mosul as well, which some experts say could help end ISIS for good.
Laura Ling explains why Mosul is such a crucial city in the fight against ISIS in this video.
Vox: The Battle for Mosul, Explained
CNN: Why the Battle for Mosul Matters in the Fight Against ISIS
The Wall Street Journal: Islamic State Hijacks Mosul University Chemistry Lab for Making Bombs