"The Syria conflict, now in its eighth year, presents significant policy challenges for the United States. (For a brief conflict summary, see Figure 2). U.S. policy toward Syria since 2014 has prioritized counterterrorism operations against the Islamic State (IS, also known as ISIL/ISIS), but also has included nonlethal assistance to Syrian opposition groups, diplomatic efforts to reach a political settlement to the civil war, and humanitarian aid to Syria and regional countries affected by refugee outflows. U.S. forces deployed to Syria have trained, equipped, and advised local partners under special authorization from Congress and, as of December 2018, have worked primarily 'by, with, and through' those local partners to retake nearly all areas formerly held by the Islamic State."
CRS Report for Congress, RL33487
Congressional Research Service: https://crsreports.congress.gov