In 2014, Islamic State militants swept into Western Iraq's Anbar Province, overrunning Iraqi security forces, enslaving minorities, and causing thousands to flee for their lives.

The jihadist group captured Iraq's largest city, Mosul, and the cities of Ramadi and Fallujah, where hundreds of US troops died fighting the Islamic State's predecessor.

Now, two years later, the Iraqi security forces, with help from Iranian-supported Shiite militias and US military advisors and warplanes, are fighting to take back towns and cities in Anbar, one battle at a time.

But it's a difficult task: Anbar has been the crucible of Iraq's insurgency, and is the country's Sunni heartland — long marginalized by and hostile to the Shiite-led government in Baghdad.