Airstrikes on ISIS, and air drops for the people the militants have trapped, began Friday. They will likely continue for months.
On Saturday evening, there was word of new U.S. airstrikes, this time targeting ISIS armored personnel carriers.
The ISIS militants are members of the Sunni branch of Islam, at war not just with Iraq's Shiite majority, but also with other ethnic and religious minorities, including Kurds, Christians and Yazidis.
American F/A-18 fighter jets are flying over Iraq once again - this time targeting ISIS militants.
The aim is to help Kurdish soldiers - the only force on the ground in northern Iraq still doing battle with the Islamic extremists.
But the Kurdish fighters retreated this week after ISIS seized more towns and captured Iraq's biggest dam.
There are now fears the militants could use the dam as a weapon, flooding hundreds of square miles of land.
In a frenzy of violence, ISIS surged into northern Iraq two months ago.
It's carried out public executions, targeting religious minorities, including Iraqi Christians.
Thousands of Yazidis, members of another religious group, fled the militants, and are now stranded on a remote mountaintop.
Only food and water drops, including by U.S. planes, are keeping them alive.
A Kurdish aid flight had to fight off an attack by ISIS on Saturday before managing to rescue a handful of Yazidi families.
Retired U.S. Army Col. Harry Schute took part in the U.S. invasion of Iraq in 2003, and now works here as an adviser to the Kurdish government.
"This is a potential disaster of epic proportions," he said.
Are the American airstrikes enough to defeat ISIS in Iraq?
"No. Not by themselves," said Schute. "A lot more needs to be done. And they would need to be a lot more sustained as well."
But the U.S. airstrikes have given Kurdish fighters breathing room. The hope is that they will now regroup and begin pushing back the ISIS militants.