People’s Protection Units (YPG)

In October of last year, the Kurdish-led Syrian Democratic Forces (SDF), backed by the United States, liberated the city of Raqqa from the Islamic State, who had proclaimed it to be the capital of its caliphate. Four months later, NATO member Turkey has opened a military campaign in the Syrian region Afrin against the same Kurds who led the fight against ISIS.

In the effort to fight ISIS in Syria, the U.S. government has recently approved supplying arms to Kurdish YPG fighters. But a key NATO ally, Turkey, has condemned the action, claiming the U.S. is empowering the PKK, a Kurdish terrorist group. Here is what you should know about the Kurdish fighters involved.