RABIA — In late September 2014, as the international coalition began to engage the Islamic State (ISIS) in earnest, Iraqi Kurdish fighters and Syrian forces seized Rabia, a city near the Iraqi-Turkish border.

It was a huge victory — one of the first in the long war against ISIS. And it may not have been possible without the assistance of another key group: the Shammar, a powerful tribe from the border regions of northern Syria and Iraq.

"Rabia has been liberated, and the Shammar closely cooperate with the Kurdish Peshmerga," said Abdullah Yawar, a Shammar tribal leader, after the successful battle.

That battlefield cooperation was the beginning of a closer alliance, sealed in October 2015 with the formation of the Syrian Democratic Forces (SDF). The SDF is made up of Syrian Kurds from the People's Protection Units (YPG), Syriac Christian militias, and Sunni tribal fighters like the Shammar.

The Shammar are one of many nomadic tribes that trace their roots to present-day Jordan and Saudi Arabia, and number 14 million people today spread between Syria and Iraq but primarily in the Iraqi cities of Fallujah, Mosul, and Sinjar. Along with their Yazidi and Christian neighbors, they have been victims of atrocities by ISIS since the fall of Mosul in June 2014.

"Emergency forces"

It was then that the tribe decided to arm itself and fight the Islamic State in the Nineveh plains in northern Iraq, allying with Kurds both at home and across the border.

The Shammar are proud of their close ties with Jordan and Saudi Arabia, and make a point of emphasizing the ethnic diversity of the SDF coalition. "We aren't a government army, we're tribal fighters," says the Shammar leader Sheikh Hamdi Daham Al-Hadi. "We call ourselves Al-Fasah, the emergency forces."

Al-Fasah controls as many as 6,000 fighters, and receives weapons and supplies from Saudi Arabia and other wealthy donors in the Gulf states. "Tribes and clans follow their own interests. If they align with ISIS, then they fight with them. But if they align with Syrian leader Bashar al-Assad then they help the regime," says Al-Hadi.

In Syria, for example, the Shammar fight beside the Kurdish YPG. But in Iraq they fight alongside the YPG's rivals, the Kurdish Peshmerga of Masoud Barzani.

Despite the overlapping allegiances, they all have a common enemy: the Islamic State. This strengthens the anti-ISIS alliance, as the inclusion of a Sunni tribe like the Shammar weakens ISIS' claim of representing downtrodden Sunnis. The Shammar often take the lead in the frontlines, coordinating offensives with their SDF allies and U.S. special forces.

This war may be their present, but the tribe is already looking toward the future. "We hope the foreign intervention will be carried out responsibly, and that the Syria of the future will be controlled by Syrians: Druze, Alawites, Kurds, Shia, and Sunnis alike," says Al-Hadi. "We live in an era of globalization, but federalism can provide new opportunities and help us avoid dictatorship."