In parts of Syria dubbed “de-escalation zones” by the government, what could yet prove a new regional conflict is escalating fast.

Its protagonists, Turkey on one side and the Syrian government with its Russian backers on the other, had only a few months ago looked open to forging a new alliance. Instead, they are now killing each other’s troops and are at each other’s throats.

This latest instalment in Syria’s war points to a much broader picture across the Middle East. As the US pulls back and loses interest, the complexity of regional conflict is escalating quickly...