For one American military veteran, joining the fight in Syria against the Islamic State (IS) was as easy as answering a Facebook ad and booking a flight.

The veteran, using the alias "John," described his unique experience as a fighter alongside the Kurds in an interview published earlier this month.

John explained that a Kurdish group known as YPG were recruiting foreign fighters via social media.

"There was a Facebook page for it -- shot them a message, expressed my interest, they got back to me, told me to send them, essentially, a resume for their vetting purposes," he told Fox News in an exclusive interview.

"What I believe is that they are European go-betweens, they are not in Kurdistan, they operate receiving information of interested Westerners, and then they either relay it or make a decision themselves of whether or not this person is suitable to work with the YPG," he explained.

"They sent (a) message saying I was approved and someone would be waiting on me."

John booked a flight to Iraq with ease.

"I just went online and bought a ticket," he admitted. "It was that easy. It was like booking a flight to Miami Beach."

In Syria, John met other Americans, a Canadians, Britons, and other foreigners who had joined the fight against IS.

"I got in a car and there was a guy from Scotland there," he recounted. "So that was kind of refreshing, to see that I'm not the only one. And it helped affirm to me, hey, I actually am with the good guys."

An estimated 1,000 foreigners are entering Syria each month to fight against IS. The makeshift soldiers are poorly equipped, however, and receive no training. John fashioned a Bible into chest armour because there were no bulletproof vests.

"It's extremely dangerous in that they're taking anyone with no military experience, no age requirements, no physical restrictions," he said. "They are just taking people there, giving them a gun, saying hey good luck buddy."

The State Department strongly discourages Americans from entering foreign armies, although it is not a crime. It is unclear if the act is a violation and whether there will be legal ramifications for people like John.

"The amount of trouble I could be in is, you know, still up in the air," he admitted. "It's a legal gray area, what I did."

After a bounty was placed on his head by IS, John sought out the U.S. Consulate in Iraq and went home.

"I told them I'm an American first," he said.