Abstract
This paper investigates the strategic consequences of the tactical alliance between the US-led international coalition against Islamic State and the Syrian Democratic Forces (SDF). The military cooperation between the coalition and the Syrian Kurds fighting Islamic State initiated during the battle of Kobane in 2014. Over the subsequent years, the cooperation turned into a more formal alliance as the US stepped up its support for the SDF deploying military personnel to Syria and providing the SDF with heavy military equipment. Applying a strategic interactionism approach, the paper argues that the alliance succeeded in defeating Islamic State. However, allying with the SDF dragged the US into the power play of the Kurds in Northern Syria. This did not only stress the US relationship with NATO ally Turkey, but it also implied frictions with Russian forces along the Euphrates River.