Much has been made of Iraq’s ethnic Kurds’ role in fighting the Islamic State of Iraq and al-Sham (ISIS), a group of Sunni jihadists aiming to overthrow Prime Minister Nouri al-Maliki’s government. While the Kurds struggle to establish their own government, they have also provided valuable military resistance the Iraqi army could not.

As news surfaced of ISIS taking over large Iraqi cities like Mosul and Tikrit, the mass flight of Iraqi soldiers to avoid fighting ISIS made way for the Kurdish Peshmerga forces to take over. Unlike the Iraqi army, the Peshmerga have continued their resistance and held ISIS off in key territories, denying them access to roads that lead to the capital, Baghdad. According to senior Kurdish leaders speaking to Vice, the strength of the Peshmerga have led to ISIS claiming they would not attack Kurdish areas, instead focusing on regions under the control of the Iraqi army, which are deemed easier to conquer. Kurdish leaders are not convinced that ISIS is being forthcoming by issuing such a promise, however, and are preparing to fight the terrorists.

Warnings from Pershmerga leaders as to the resilience of ISIS have become increasingly alarming as ISIS takes more territory from the Iraqi army. Polad Talabani, the leader of the Peshmerga forces, told NBC this week that the struggle to keep ISIS at bay has only become more difficult. While the Kurds have “inflicted heavy casualties” on ISIS, according to the leader, every time they believe they have delivered a decisive blow on the terrorist paramilitary, “dozens more will appear from nowhere to flood the battlefield.”

The Peshmerga, NBC reports, are concentrating on keeping ISIS away from major roads that lead to Baghdad. Any significant coup by ISIS on one of these roads could trap the capital’s population and give the jihadists unwanted access. Forty thousand Kurds are reportedly fighting ISIS. While the exact number of ISIS members is unknown, the population of its members globally is believed to be in the thousands, spread across Iraq and Syria.

Another senior leader of Kurdish government, Rooz Bahjat, describes the struggles of Kurdish soldiers as a battle against jihadists who come to the battlefield to die, making it difficult to capture ISIS forces without killing them. “The hard part is killing somebody who already wants to die,” he explains, adding that an ISIS fighter’s “only goal or mission in life is to get killed in the fight.”

Below, watch NBC’s report on the Kurdish Peshmerga: