Mosul is ISIS’s last remaining stronghold in Iraq, and there’s a good reason why the operation to kick them out is getting such massive coverage lately in a country that most of America hasn’t though about too much for years.

Mosul is the second largest city in Iraq, and it fell to ISIS back in June 2014. It is about 260 miles north of Baghdad and is close to the borders of Turkey and Syria, the latter of which has seen a huge surge in ISIS in recent years. Mosul is also important because it is near major oil fields and an oil pipeline that runs into Turkey.

The Iraqi army surrendered control to ISIS back in 2014 after an invasion by militants, which later claimed to have set up an Islamic state or caliphate there. But earlier this week, Iraqi forces moved in aggressively in an attempt to reclaim the city. With ISIS already reeling from losses of Iraqi cities like Fallujah and Tikrit, losing Mosul as well would be a massive blow to the organization.

Authorities believe there are between 3,500 and 5,000 ISIS fighters in Mosul. That is much smaller than allied forces, but because they are entrenched in the city and use suicide bombs, booby traps and other tactics, they remain extremely dangerous and difficult to root out.

Mosul is a shell of its former self, with only 1 million residents still living there out of the 2.5 million that was there in June 2014 when ISIS took over. There have been public beheadings and the enforcement of sharia law in the two years since.