Four years ago, the Islamic State of Iraq and the Levant group (ISIL, also known as ISIS) began a series of lightning advances across Iraq and Syria, taking advantage of regional instability to make rapid territorial gains. Since then, there have been hundreds of battles, gruesome killings and a US-led campaign of air attacks. Today, ISIL is a group in decline, driven out of its urban strongholds as local and international forces reclaim key territory.

Al Jazeera examines the key events in ISIL's rise and fall.