Aaron Core thought he had seen enough of Iraq during a U.S. Army tour that ended in 2010. But the image of American journalist James Foley being murdered by an ISIS executioner prompted him to leave Tennessee and head back, this time as an unpaid volunteer in the service of the Kurdish Peshmerga.

"There's evil in this world that needs to be dealt with,"

- Kurt, US volunteer fighting alongside Kurdish Peshmerga

The 27-year-old Chattanooga resident and former Army National Guard specialist spoke to FoxNews.com at a Kurdish base near Kirkuk, where he has served since last fall, taking part in numerous firefights with ISIS as the Kurds battle to stop the terrorist army's caliphate from encroaching on its territory in the nation's north.

“When I heard they had their first American victim, I had to come back,” he said, referring to Foley, who was beheaded in a grisly video posted online by ISIS last August. “I had to.”

An American flag patch sits on Core’s shoulder, just above one bearing both the American and Kurdish flag representing his status as a volunteer with the Kurdish Peshmerga. Core isn’t alone. When FoxNews.com spoke to Core, two other Americans who did not give their last names, sat nearby. Taylor, a 23-year-old veteran from Texas, and Kurt, a 25-year-old U.S. Marine from Washington state, said they were also drawn to the region by a need to stand up to the barbarity of ISIS.

“I decided I wanted to make a difference and fight Daesh [Arabic slang for ISIS] and support the Kurdistan people in their struggle, so I bought a ticket,” Kurt said. 

Taylor, a former Army soldier, said he was back home working at a minimum wage security job when he decided the skills he acquired in the U.S. military could be best put to use fighting with the only army that seemed to be standing up to ISIS.

The U.S. State Department does not support or encourage Americans traveling to Iraq to volunteer, but has not stopped many from doing just that. Since the Syria-based Islamic State’s invasion of Iraq in June 2014, the Peshmerga have so far been successful in stopping ISIS advances further into Kurdish territory, yet they are far from defeating the Islamic terror group. The Islamic State fighters, who include men tested on the battlefields of Syria as well as many former members of the Iraqi military, are a formidable foe.

“They’re no joke,” said Kurt. “They’re very disciplined, highly effective fighters. If we’re not careful, they’ll win.”

While the help from Western volunteers is welcomed by the Kurds, many more Westerners have chosen to fight with ISIS, an irony not lost of Kurdish Brig. Gen. Aris Kadhr of the 9th Brigade.

“Most of the people from your countries who have come to volunteer with the Peshmerga have come to fight the people from your countries who have joined ISIS,” Kadhr told FoxNews.com.

The Kurds, who have engaged in several firefights with the jihadi fighters over recent months, often in defense of oil production facilities in Kirkuk, need more than just volunteers, said the general.

“We still need more help from the International coalition, we need more weapons, more advisers and good training,” Kadhr said.

The coalition of nations, including the U.S., has provided air support to help the Peshmerga hold off ISIS' advances. But the Peshmerga still rely on military aid that is passed through the central Iraqi government in Baghdad, a process proving to be too little and too slow for the Kurdish forces and American volunteers on the front lines.

“Gear keeps you alive," Core said. "We need plate carriers, something to stop the bullet or at least slow it down. Medical equipment, vehicles.

"That’s the key to war, is to stay alive,” he added.

While bulletproof vests and armored vehicles seem like practical needs for the volunteers, there are a few creature comforts that they have on their minds.

“Nutella,” Core laughed. “There’s things like bacon and cheeseburgers.”

Kurt agreed that things Americans take for granted are the hardest to do without.

“All we ever talk about on our downtime is the things we can’t get here," he said. "It makes it horrible.”

Leaving behind family to fight another nation's war is a sacrifice that takes its toll on the volunteers' loved ones, too.

“My mom was pissed," Core said. "She wasn't too happy, but she completely understands why I’m out here.” 

Taylor said he couldn't bring himself to tell his mother what he is up to, especially given that he made the trip on May 10.

“It was Mother’s Day, so I didn’t think that was a good idea to tell her then,” he said.

Kurt has no idea how long he will be in Iraq, or if he will ever make it home. But he feels he is answering a call that he cannot ignore.

"There's evil in this world that needs to be dealt with," Kurt said.