Major powers involved in the Syrian war are racing to maximize gains from the crumbling Islamic State in southern and eastern Syria. The continued advancement of pro-Syrian regime forces and Iranian-backed militias toward the US-held Tanf base – as well as the potential advance of both sides toward the Iraqi border area – raise the risk of further clashes that may draw in the US and Russia, though the latter has been unwilling to challenge US strikes against a pro-regime convoy and Syrian warplanes this year.