John Kerry does not give up easily. On Thursday in Munich the US secretary of state will promote a fresh diplomatic effort on Syrian peace talks. Yet for all his determination, events on the ground are not only working against a breakthrough, but raising increasingly profound doubts about the coherence of US and western strategy. For more than a week, the rebel-held city of Aleppo, once Syria’s largest, has been pounded by Russia’s air force, acting in support of Iranian-backed militias and Syrian government troops. If this annihilation strategy continues, the balance of forces in Syria’s civil war will change fundamentally. Mr Kerry’s proposed negotiated solution will be null and void, for there will be no Syrian opposition force left to be represented at any negotiating table.