Former British soldier Jim Matthews will be prosecuted under the country's Terrorism Act of 2006 and will appear in court tomorrow to be formally charged with "attending a place or places in Iraq and Syria where instruction or training was provided for purposes connected to the commission or preparation of terrorism." Matthews will be the first British national on record to face terrorism charges for fighting among the ranks of the People's Protection Units (YPG), the Syrian affiliate of the PKK terrorist organization.

At the same time, the British man's prosecution promises to challenge conventional wisdom about foreign terrorist fighters. In recent years, the issue has been typically associated with non-nationals of Syria and Iraq traveling to the conflict zone in order to join Daesh. Meanwhile, Western officials and media outlets often used the term volunteers to describe foreign terrorist fighters relocating to Syria and Iraq after being recruited by the PKK and YPG in Europe and elsewhere.

Hundreds of Westerners are believed to have joined and received weapons and explosives training from the YPG in Syria in recent years. According to the Henry Jackson Society, a think tank based in London, approximately 80 percent of all foreign fighters fighting in the YPG ranks come from English-speaking countries. In recent weeks, PKK and YPG foreign fighters have reportedly traveled to Afrin, where Turkish forces and the Free Syrian Army (FSA) have been fighting YPG militants since Jan. 20. This development established that the involvement of Westerners radicalized and trained by the group was not limited to the fight against Daesh.

In addition to fueling diplomatic tensions with Turkey, a NATO ally, a failure to prosecute foreign fighters returning to their native countries after fighting among the YPG could pose a serious threat to Europe's security. It must be understood that those foreign fighters will reasonably maintain their links with the PKK and YPG upon their return, and engage in various activities in Europe at the request of the organization, recruiting, fundraising and even carrying out terrorist attacks against perceived enemies.

European governments cannot afford to forget that those individuals, once radicalized, become members of seemingly unrelated organizations. A case in point concerns a Turkish national who was arrested in 2007 for his links to left-wing extremists before carrying out several bombings in Turkey on behalf of Daesh a decade later.

To ensure that foreign fighters returning home after fighting within the YPG ranks in Syria do not radicalize a new generation of young Europeans, all concerned countries must follow in the U.K.target="_blank"'>