President Trump is right: People are sick and tired of expensive and seemingly never-ending U.S. military deployments. Mission creep, conflating initial war aims in Afghanistan and Iraq with nation building, cost trillions of dollars and several thousand lives. But even by realist standards, which downplay the importance of maintaining an alliance with Syrian Kurds, acquiescence to Turkish demands could have consequences far beyond Turkey.

Speaking at the Herat Security Dialogue late last week, Roland Kobia, the European Union’s special envoy for Afghanistan, declared that for Europeans “diplomacy is in our DNA.” But diplomacy is not a catch-all, like its supporters claim. When all parties are sincere in their desire for conflict resolution it works, but other regimes and terrorist groups see the Western commitment to diplomacy as a weakness to exploit.