I (Joseph Votel) first met General Mazloum Abdi at a base in northern Syria in May 2016. From the start, it was obvious he was not only an impressive and thoughtful man, but a fighter who was clearly thinking about the strategic aspects of the campaign against ISIS and aware of the challenges of fighting a formidable enemy. He could see the long-term perils from the civil war, but recognized that the most immediate threat to his people was ISIS. After a fitful start in Syria, I concluded that we had finally found the right partner who could help us defeat ISIS without getting drawn into the murkier conflict against Bashar al-Assad’s regime.

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The Syrian Democratic Forces (SDF), initially composed of the Kurdish People’s Protection Units (YPG), was then conceived: a fighting force that eventually grew to 60,000 battle-hardened and determined soldiers. The decision to partner with the YPG, beginning with the fight in Kobane, was made across two administrations and had required years of deliberation and planning, especially given the concerns of our NATO ally Turkey, who regards the SDF as an offshoot of the designated terrorist group the Kurdistan Workers’ Party (PKK). Eventually, the YPG became the backbone of the fighting force against ISIS in Syria. Without it, President Donald Trump could not have declared the complete defeat of ISIS.

With support from what grew to be the 80-member Coalition to Defeat ISIS, which included air power, advisers on the ground, and equipment, the SDF became a force to be reckoned with and led a string of victories. In August 2016, it liberated the Syrian town of Manbij, which once functioned as a hub for ISIS fighters to cross into Turkey and is believed to be where the attackers who carried out the November 2015 Paris attacks transited. Mindful of the need for credibility as it pushed to liberate Arab-dominated areas, the YPG had succeeded in incorporating Arab units into its structure as a united Arab-Kurd fighting force. That force, the SDF, went on to liberate the so-called capital of the caliphate, Raqqa, and towns in the Middle Euphrates River Valley, culminating in the territorial defeat of ISIS in Baghouz this past March.

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Over four years, the SDF freed tens of thousands of square miles and millions of people from the grip of ISIS. Throughout the fight, it sustained nearly 11,000 casualties. By comparison, six U.S. service members, as well as two civilians, have been killed in the anti-ISIS campaign. Key to this effective relationship was mutual trust, constant communication, and clear expectations. The partnership was not without its difficulties. That included working through the December 2018 announcement of our sudden departure and our subsequent agreement with Turkey to pursue a security mechanism for the border areas. But each time, the strong mutual trust built on the ground between our military members and the SDF preserved our momentum. The sudden policy change this week breaks that trust at the most crucial juncture and leaves our partners with very limited options.