A former British marine  became the second Westerner killed while fighting for Kurdish forces against the Islamic State group. Konstandinos Erik Scurfield, 25, was killed while fighting in an area west of the Syrian city of Qamishli earlier this week. He was one of around 100 Westerners fighting alongside the 30,000-strong Kurdish peshmerga forces, according to the BBC.

While governments and media have made much of Westerners joining the Islamic State group, Scurfield’s death highlights a similar situation on the other side: Former soldiers and even ordinary citizens from Western nations are travelling to fight against the extremist group, also known as ISIS, in Syria and Iraq. 

The Kurdish Popular Protection Units (YPG) said that Scurfield made the journey in December after finishing service with the Royal Marines in the United Kingdom, according to the group’s Facebook page.

“He was martyred during a bloody battle with ISIS forces in an attempt to liberate the village of Xezale near Til Berak in the Rojava enclave (western Kurdistan),” said a YPG spokesperson on the Facebook page, which had 66,000 likes as of March 5.

His death comes just one week after the death of Australian Ashley Johnston, also known by the Kurdish name Heval Bagok Serhed, who was killed while fighting the Islamic State on behalf of YPG.

Both men were part of a foreign fighter group known as the “Lions of Rojava,” which according to its Facebook page aims to send “terrorists to hell and save humanity.” 

While the full details of those 100 Western fighters are not fully known, media reports indicate that they are from Australia, Great Britain, the U.S. Germany, Spain, France, Canada, Israel and the Netherlands. Among them are a 17 year-old from London, a biker gang from Germany and former U.S. military personnel.  

Jason Matson, a former U.S. Army soldier fighting in the Lions of Rojava (Rojava is a region of Kurdistangroup, said he was drawn to the fight by a sense of duty towards the Kurds because of their loyalty to the U.S. during the Iraq war. "I'm not going back until the fight is finished and ISIS is crippled," Matson said to the Associated Press in early February. "I decided that if my government wasn't going to do anything to help this country, especially Kurdish people who stood by us for 10 years and helped us out while we were in this country, then I was going to do something."

Matson, three other Americans and an Australian said they joined the group after contacting them through Facebook.

Westerners with past military experience are highly sought by Kurdish forces, as they can train the many Kurdish fighters who have little or no experience, and are often as young as 17, said Western ex-soldiers cited by the AP. With no body armor and just the weapons they take from dead Islamic State fighters, the young soldiers are taught the basics of how to act in battle. 

Some of those Western volunteers are breaking the law to go fight with the Kurds. Not all countries allow their citizens to fight for other nations, or militia groups.

The U.S. State Department considers the Turkey-based Kurdish Workers Party, also known as the PKK, a terrorist organization, but the U.S. government has not banned Americans from fighting alongside militia groups that are linked to it. According to U.S. law, Americans can fight for other countries and groups as long as those groups are not fighting against the U.S.

Australia, on the other hand, has specific rules against citizens fighting with any group outside of the Australian military. It also was the first country to criminalize travel to Syria’s al-Raqqa province, the de facto capital of the s-called Islamic State.

The rules used to stop people from joining the Islamic State group have not been applied equally to those travelling to join Kurdish fighters. BBC security correspondent Frank Gardner said that if any British person was suspected of trying to join ISIS, they would get their "collar felt at Heathrow," London's main international airport, and yet there "seems to be a silence about people going to fight on the other side."

But the notion of fighting in other people's wars is not unique to the conflict unfolding in the Middle East. Just one week ago, Spanish authorities arrested eight people who, the government said, had been fighting for pro-Russian rebels in East Ukraine. The police used information gathered from social media to make the arrests.